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    • 专利摘要:
    Catalyst and its use in purification of contaminated water. The present invention relates to a catalyst comprising a noble metal, preferably palladium, incorporated on indium oxide (in2 o3), which acts as a catalytic active support, its procedure of obtaining and its use in a process of purification of contaminated waters. This catalyst is especially interesting for the elimination of nitrate (no3-), reaching selectivities to nitrogen gas (n2) elevated and close to 100% at high conversion values. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2634326A1
    申请号:ES201630227
    申请日:2016-02-26
    公开日:2017-09-27
    发明作者:Alejandro HERRERO PIZARRO；Víctor Manuel MONSALVO GARCÍA；Irene TORIJA JUANA；Jesús ARAUZO PÉREZ
    申请人:Abengoa Water SL；
    IPC主号:
    专利说明:

    The present invention relates to a catalyst comprising a noble metal,preferably palladium (Pd), incorporated over indium oxide (In2O3), which actsas a catalytic active support, its method of obtaining and its use in aPolluted water purification procedure. This catalyst isespecially interesting for nitrate removal (NO3-), reaching
    10 gas nitrogen selectivities (N2) high and close to 100% at high conversion values. STATE OF THE TECHNIQUE
    15 Water pollution is an environmental problem that requires the development of effective systems for its treatment. The presence of nitrate (NO3-) in these waters is a well known fact, which has been associated with the use of nitrogen fertilizers as well as other agricultural and industrial activities.
    20 Both the conversion of nitrate (NO3-) to nitrite (NO2-) (catalytic reduction) and the selectivity to nitrogen gas (N2) are important factors to achieve the total purification of the water to be treated, since the legal concentration limits for nitrite (NO2-) and ammonium (NH4 +) established in water intended for human consumption are more restrictive than for nitrate (NO3-), both in the European Union and in others
    25 countries (0.1 mg / L and 0.5 mg / L, respectively).
    During the last years, different techniques have been developed for the elimination of nitrogenous species such as nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +), especially non-destructive processes of ion exchange and separation
    30 with membranes. The most widely implemented destructive methods are based on the elimination of nitrate (NO3-) through biological systems while physicochemical and catalytic processes have been studied to a lesser extent. Among the latter, the use of iron salts or zero-valent iron, photoreduction and catalytic reduction of nitrate (NO3-) stand out.


    By catalytic reduction, both nitrate (NO3-) and nitrite (NO2-) can be removed from water using a reducing agent such as hydrogen (H2), formic acid (CH2O2) or hydrazine (N2H4) using a catalyst suitable. However, the process results in the formation of ammonium (NH4 +) as a desired by-product. Therefore, the catalyst used is one of the key factors for the development of this process to achieve maximum selectivity towards nitrogen gas (N2). Catalysts based on supported noble metals only had characteristics suitable for the hydrogenation of nitrite (NO2-). It is necessary, therefore, the development of bimetallic catalysts to remove nitrate
    10 (NO3-) and in turn achieve high selectivity towards nitrogen gas (N2).
    In this sense, bimetallic catalysts that consist of two different active phases, a transition metal such as copper (Cu), tin (Sn), indium (In), silver (Ag), gallium (Ga), or iron, have been traditionally used (Fe), among others and a noble metal 15 such as palladium (Pd), rhodium (Rh), ruthenium (Ru), platinum (Pt), or iridium (Ir), in which the function of the transition metal is that of reduce the nitrate molecule (NO3-) to nitrite (NO2-), while the function of the noble metal is to regenerate the reducing power of the transition metal and hydrogenate the nitrite molecule (NO2-) to ammonium (NH4 +) or nitrogen gas (N2) this being the desired reaction product in the
    20 decontamination of nitrate contaminated water (NO3-) by removing nitrogen from water [Hörold, S., Vorlop, K.D., Tacke, T., Sell, M., Catal. Today 17, 21 (1993)].
    The main difficulty to overcome in the development of this type of catalysts has been to achieve a high selectivity to nitrogen gas (N2) avoiding the formation of ammonium
    25 (NH4 +) and the consequent rise in pH associated with the formation of hydroxide ions (OH-) during hydrogenation of nitrite (NO2-). This rise in pH can be avoided by adding acidifying agents such as carbon dioxide (CO2) that forms carbonic acid (H2CO3) and prevents the interaction between hydroxide (OH-) and nitrite (NO2-).
    30 On the other hand, most bimetallic catalysts are synthesized using noble metal salts, mainly palladium (Pd), being the most selective nitrogen gas (N2) than the rest of precious metals, and transition metals, mainly copper (Cu), tin (Sn) and Indian (In), which are impregnated
    35 successive, or at the same time, by co-impregnation in acid solutions or by other methods such as precipitation-deposition.


    The modification of certain reaction conditions such as the decrease in the partial pressure of hydrogen, the flow rate of the same or the pH of the reaction medium allows, in some cases, to obtain selectivities to nitrogen gas (N2) close to 100% using palladium bimetallic catalysts -metal (Pd-Me).
    5 In recent years, significant progress has been made in terms of the development of new catalysts that show greater resistance to leaching and greater selectivity to nitrogen gas (N2). Such is the case of the supported palladium-tin (Pd-Sn) and palladium-Indian (Pd-In) catalysts which, in this
    10 sense, what was achieved with the palladium-copper (Pd-Cu) catalysts initially [Barrabés, N., Sá, J., App. Catal. B: Environ. 104, 1 (2014)].
    Other catalysts are based on noble metals directly supported on reducible metal oxides, which are usually synthesized by impregnating a noble metal such as palladium (Pd) onto a metal oxide such as cerium oxide (CeO2) or oxide of tin (SnO2). This type of catalysts has higher reaction rates than those achieved with traditional bimetallic catalysts supported on inert oxides such as aluminum oxide (Al2O3) or silicon oxide (SiO2), or on other supports such as activated carbon, clays or zeolites. This difference is explained by the greater number of interactions between the active phases involved in the reduction of nitrate (NO3-), being higher in those of metal oxides. However, particularly cerium oxide (CeO2) is poisoned with the addition of carbon dioxide (CO2) to the medium, so it is not recommended for use in nitrate catalytic reduction processes (NO3-) in
    It is necessary to lower the pH values by adding CO2 [Devadas, A., Vasudevan, S. Epron, E., J. Hazard. Mat. 185, 1412 (2011)]. DESCRIPTION OF THE INVENTION
    The present invention relates to a catalyst comprising nanoparticles of a noble metal, preferably palladium (Pd), deposited on indium oxide (In2O3) (also known as indium sesquioxide) which acts as active catalytic support, its method of obtaining and its use in a polluted water purification procedure. This catalyst is especially interesting for the
    35 nitrate removal (NO3-), with selectivities reaching nitrogen gas (N2) high and close to 100% at high conversion values, compared with


    values achieved with other catalysts. It is also suitable for the reduction of halogenated compounds such as chlorinated herbicides, halogenated contaminants, trihalomethanes and other by-products of drinking water disinfection such as bromate (BrO3-), chlorate (ClO3-), etc. It can also be used in rust processes
    5 reduction in which both active phases are necessary. You can alsouse in turn for the decomposition of hydrogen peroxide (H2O2).
    This type of catalytic support based on indium oxide (In2O3) is characterized by a small surface area, less than 20 m2 / g, and a pore size between 20Å and 400Å.
    10 In the case where the Pd catalyst deposited on In2O3 is not supported, the catalyst thanks to the support of In2O3 allows to effectively neutralize the OH-generated hydroxyl groups during the hydrogenation of nitrite (NO2-), by adding carbon dioxide (CO2) or other acidifying substance in the reaction medium.
    This catalyst, in which all the metal is in contact with the oxide, also achieves the removal of nitrate (NO3-) in aqueous media without the need to adjust the pH of the medium. On the other hand, the use of the catalyst with pH adjustment allows to reach the legal limits of ammonium (NH4 +) in drinking water, that is, ammonium concentrations (NH4 +) below 0.5 mg / L.
    Thus, a first aspect of the invention relates to a catalyst comprising a noble metal of group VIIIB of the Periodic System of the Elements in the form of spherical monometallic nanoparticles of size between 2 and 20 nm uncoated, which are found in direct contact with a surface of
    25 indium oxide that acts as a support.
    In a preferred embodiment, the noble metal of group VIIIB of the Periodic System of Elements used is selected from palladium (Pd), platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), in its zero-valent state, in any of its states of
    30 more stable oxidation, or in any of the possible combinations; and in a more preferred form palladium (Pd) is used.
    In a more preferred embodiment, the proportion of noble metal is between 0.1% and 30% by weight with respect to the weight of the catalyst.
    In another preferred embodiment, indium oxide (In2O3) can be used both in its crystalline and amorphous form.


    In another preferred embodiment, the catalyst may be supported. These supports are selected from alumina, silica gel, zeolites, clays, cordierite or metallic ceramic monoliths of Fecralloy® (iron / chrome / alumina alloy), ceramic or polymeric membranes, ceramic, metal or polymeric extrudates.
    5 different forms such as spheres, granules, pearls, cylinders, hollow cylinders, or hollow spheres, among others.
    In the present invention, "monometallic nanoparticles" means those nanoparticles that are composed exclusively of a single noble metal,
    10 depending on the starting product of the catalyst synthesis, and which is not forming an alloy with other metals or with the indium (In) from the active support of indium oxide (In2O3) of the catalyst.
    A second aspect of the present invention relates to a process for obtaining the catalyst of the invention comprising the following steps:
    (to) incorporation of the noble metal on indium oxide (In2O3);
    (b) drying of the product obtained in step (a) at a temperature between 25 ° C and 200 ° C;
    (C) calcination between 200 ° C and 600 ° C of the product obtained in step (b).
    In a preferred embodiment, a subsequent step of activating the product obtained in step (c) is optionally carried out by applying hydrogen (H2) from 25 ° C to 250 ° C, preferably between 25 ° C and 120 ° C.
    In another preferred embodiment the noble metal of group VIIIB of the Periodic System of Elements employed in step (a) is selected from palladium (Pd), platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh ), in its zero-valent state or in any of its most stable oxidation states, or any of the possible combinations; and in a more preferred form palladium (Pd) or its precursor salts is used.
    30 The palladium precursor salts mentioned are selected from the following list: palladium chloride (PdCl2), palladium nitrate (Pd (NO3) 2), sodium tetrachloropallate (II) (Na2PdCl4), palladium acetate (Pd (OAc ) 2), tetramin palladium nitrate (Pd (NH3) 4 (NO3) 2) and palladium hexafluoride acetylacetonate (Pd (hfa) 2).


    In another preferred embodiment, the incorporation of the noble metal onto indium oxide (In2O3) in step (a) is carried out by methods known to one skilled in the art such as for example wet impregnation, impregnation to incipient moisture, precipitation- deposition, chemical vapor deposition from
    5 metalorganic compounds (MOCVD) or chemical vapor deposition (CVD).In such methods, aqueous or organic solutions can be used. TheOrganic solutions can be selected from methanol (CH4O), ethanol(C2H6O) and acetone (CH3 (CO) CH3) among others or any of their mixtures.
    As indicated above, in another preferred embodiment, the catalyst may be supported. Preferably the catalyst is supported, and this support can be incorporated before or after step (a).
    When the support is incorporated before step (a), indium oxide is started
    15 (In2O3) supported. In a particular embodiment, the supported indium oxide (In2O3) can be obtained by any method known to a person skilled in the art, such as by impregnating the support with an indium salt and subsequent calcination.
    When the support is incorporated after step (a), the product obtained in step (a), which is in powder form, is incorporated on a support before carrying out step (b), said incorporation It can be performed by any deposition method known to a person skilled in the art.
    25 The previously mentioned supports are selected from alumina, silica gel, zeolites, clays, cordierite or metallic ceramic monoliths of Fecralloy® (iron / chromium / alumina alloy), ceramic or polymeric membranes, ceramic, metal or polymeric extrudates of various types. shapes such as spheres, granules, pearls, cylinders, hollow cylinders, or hollow spheres, among others.
    On the other hand, in the process of obtaining the catalyst of the invention the calcination step c) is considered essential since it allows a better distribution of the metal over the indium oxide (In2O3). The calcination of the material allows a proportion of active nanoparticles of palladium (Pd) to be formed over indium oxide
    35 (In2O3) that are not achieved in the absence of the calcination stage where the palladium salt remains precipitated on its surface in the uncalcined catalyst.


    Another advantage of the calcination stage is the elimination of certain elements of the palladium precursor salts to be used such as the removal of chlorine in the case of using palladium chloride (PdCl2) or the removal of nitrogen when nitrate is used. palladium (Pd (NO3) 2).
    In short, this process of obtaining confers on the catalyst a series of differentiating and improved characteristics with respect to the catalysts already known in the state of the art, and whose synthesis procedures differ from those described in the invention.
    In a third aspect, the invention relates to the use of the catalyst described for the removal of contaminants present in water, where the contaminants are selected from nitrate (NO3-), nitrite (NO2-), halogenated compounds from, for example, from biocides and herbicides (not limited to perchlorate (ClO4-), chlorate (ClO3-), chlorite (ClO2-), etc.), heavy metals (not limited to hexavalent chromium), and peroxides (not limited to hydrogen peroxide (H2O2) ), among others. Preferably, the contaminant is nitrate (NO3-).
    In a preferred embodiment, the process of purification of contaminated water is carried out by removing the contaminants by catalytic reduction reactions, hydrodehalogenation or both simultaneously. In this way, the removal of nitrate (NO3-), bromate (BrO3-) and chlorate (ClO3-) leads to the formation of nitrogen gas (N2), bromide (Br-) and chloride (Cl-), respectively.
    A fourth aspect of the invention relates to a process for purification of contaminated water comprising a first step of contacting the catalyst of the invention, as defined throughout the description, with the water stream at treat and a reducing agent. The water stream can be treated continuously or discontinuously.
    In a preferred embodiment, the catalyst is in a reactor selected from fixed bed reactors, fluidized bed reactors, catalytic membrane reactor and monolithic reactor.


    In another preferred embodiment, the process of purification of contaminated water consists in removing the contaminants by catalytic reduction reactions, hydrodehalogenation or both simultaneously.
    In a more preferred embodiment, the catalytic reduction reactions comprise the use of the catalyst of the invention and saturation of the medium with a reducing agent before or after contacting the catalyst with the water stream to be treated, preferably with hydrogen. gas (H2) or other reducing agents such as formic acid (CH2O2) or hydrazine (N2H4). Preferred operating conditions
    10 are between 5 ° C and 25 ° C and pressure between 1 bar and 10 bar and it is advisable to adjust the pH of the medium to values between 3 and 7, more preferably between 4.5 and 6 by acidifying agents that prevent the accumulation of hydroxyl anions (OH-) in the reaction medium.
    In a preferred embodiment, saturation of the medium is recommended when treating chlorinated or other halogenated compounds.
    In a preferred embodiment, these reactions are used for the reduction or elimination of substances such as nitrate (NO3-), nitrite (NO2-), halogenated compounds
    20 from, for example, biocides and herbicides (perchlorate (ClO4-), chlorate (ClO3-), chlorite (ClO2-), etc.), heavy metals such as hexavalent chromium and peroxides, among others. Preferably, the contaminant is nitrate (NO3-). The removal of nitrate (NO3-), bromate (BrO3-) and chlorate (ClO3-) leads to the formation of nitrogen gas (N2), bromide (Br -) and chloride (Cl-) respectively.
    Preferably, in the catalytic reduction of nitrate (NO3-) the amount of hydrogen (H2) fed to the reactor is limited to partial pressures below 0.05 or low concentrations of dissolved hydrogen (H2) are maintained, for example, unless 0.2 mg / l. The hydrogen (H2) feed is carried out by a system of
    30 permeation thereof by means of rubber or silicone membranes reinforced or not reinforced with thicknesses of less than 20 µm or by bubbling. Also, the adjustment of the amount of hydrogen (H2) is regulated by lowering the partial pressure by diluting it with other gases. More preferably, in the catalytic reduction of nitrate (NO3-) one works in a temperature range of between 5
    35 ° C and 25 ° C, without heating the reactor.


    Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the
    5 invention. The following examples and figures are provided by way of illustration andThey are not intended to be limiting of the present invention. BRIEF DESCRIPTION OF THE FIGURES
    10 FIG. 1. Difractogram of the Pd / In2O3 catalyst synthesized from palladium chloride (PdCl2) obtained by the procedure developed according to Example 1.
    FIG. 2. Difractogram of the Pd / In2O3 catalyst synthesized from sodium tetrachloropalate (Na2PdCl4) obtained by the procedure developed
    15 according to Example 2.
    FIG. 3. Stability study of Pd / In2O3 supported on Al2O3 spheres in aqueous medium for catalytic reduction of long-lasting nitrate (300 h).
    20 FIG. 4. Concentration of ammonium (NH4 +) detected at different conversions of nitrate (NO3-) during catalytic reduction of nitrate (NO3-) with palladium (Pd) catalysts on tin (SnO2) and indium (In2O3) oxides without adjustment of pH
    FIG. 5. Ammonium concentration (NH4 +) detected at different conversions of
    25 nitrate (NO3-) during catalytic reduction of nitrate (NO3-) with palladium (Pd) catalysts on indium oxide (In2O3) without and with pH adjustment with carbon dioxide (CO2).
    FIG. 6. Nitrate conversion (NO3-) versus ammonium concentration (NH4 +) during
    The catalytic reduction of nitrate (NO3-) with the palladium (Pd) catalyst on indium oxide (In2O3) with different hydrogen flow rates (H2) and pH adjustment with carbon dioxide (CO2) (CO2 flow rates). The horizontal line indicates the legal limit of concentration of ammonium (NH4 +) for human drinking water (Directive 91/676 / EEC).


    FIG. 7. Decomposition of hydrogen peroxide (H2O2) with palladium catalyst (Pd) over indium oxide (In2O3).
    FIG. 8. Nitrate conversion (NO3-) versus ammonium concentration (NH4 +) during
    5 catalytic reduction of nitrate (NO3-) with palladium (Pd) catalysts overindium oxide (In2O3), Pd-In on alumina (Al2O3), Pd-In on silicon oxide(SiO2) and Pd on tin oxide (SnO2) under the same conditionsExperimental
    10 FIG. 9. Conversion of nitrate (NO3-) to ammonium concentration (NH4 +) during catalytic reduction of nitrate (NO3-) with palladium (Pd) catalysts on indium oxide (In2O3) with and without prior calcination.
    FIG. 10. View of Pd nanoparticles in the support synthesized on In2O3 in the
    15 which shows spherical morphology with nanoparticle sizes between 2 and 10 nm.
    FIG. 11. View of the Pd nanoparticles in the support synthesized on In2O3 in which spherical morphology with nanoparticle sizes between 2 and 10 can be seen
    20 nm EXAMPLES
    The invention will now be illustrated by tests carried out by the
    25 inventors, which shows the effectiveness of the process, product and use of the invention.
    Example 1. Synthesis of a catalyst of Pd / In2O3 from palladium chloride (PdCl2)
    The palladium (Pd) catalyst is synthesized using indium oxide (In2O3) as an active support whose particles have an approximate diameter of about 100 nm.
    Palladium (Pd) was incorporated into the support by wet impregnation, reaching
    35 5% palladium (Pd) by weight. The precursor palladium salt used was palladium chloride (PdCl2) dissolved in water with hydrochloric acid (HCl, 0.2 M). A


    1 ml volume of this solution per gram of indium oxide (In2O3). After impregnation, the resulting material was dried for 17 hours at 90 ° C and calcined at 500 ° C for 2 h in air.
    5 Optionally, the catalyst can be reduced to 100 ° C or at room temperaturefor one hour before use.
    Figure 1 shows a diffractogram of the catalyst synthesized according to this procedure. The Intensity (I) appears on the ordinate axis, which is measured in 10 accounts or accounts per second.
    By X-ray diffraction, peaks corresponding to indium oxide (In2O3; reference number 00-022-0336) and palladium (Pd; reference number 00-046-1211) have been identified, according to Prewitt, et al. . Inorganic Chemistry, 1969, 8 (9), 15 1985-1993 and Kumar, J. et al. Journal of the Less Common Metals, 1989, 147 (1), 59-71.
    On the other hand, the peaks with little width that are observed in Figure 1 denote the high crystallinity of indium oxide (In2O3), greater than 90%.
    20 It also reports on the size of Pd crystals, between 2 and 20 nm, being comparable to the data obtained with other techniques such as TEM.
    The catalyst obtained has a BET area (Brunauer-Emmett-Teller) of 3 m2 / g and an average pore size of 139 Å.
    Example 2. Synthesis of a Pd / In2O3 catalyst from sodium tetrachloropalate (Na2PdCl4)
    Palladium (Pd) catalyst is synthesized using indium oxide (In2O3) as an active support whose particles have a diameter of about 100 nm.
    Palladium (Pd) was incorporated into the support by wet impregnation, reaching 5% palladium (Pd) by weight. The salt used was sodium tetrachloropalate (Na2PdCl4) in water. A volume of 1 ml of this solution was used per gram of
    35 indium oxide (In2O3). After impregnation, the resulting material was dried for 17 hours at 90 ° C and calcined at 500 ° C for 2 h in air.


    This procedure was carried out for the synthesis of the catalysts with other supports instead of indium oxide (In2O3) such as tin oxide (SnO2), silicon oxide (SiO2) or aluminum oxide or alumina (Al2O3).
    5 Optionally, the catalyst can be reduced to 100 ° C or room temperaturefor one hour before use.
    Figure 2 shows a diffractogram of the Pd / In2O3 catalyst synthesized according to this procedure. The Intensity (I) appears on the ordinate axis, which is measured in 10 accounts or accounts per second.
    By X-ray diffraction, peaks corresponding to indium (In2O3) and palladium (Pd) have been identified in the same manner as indicated in Example 1.
    On the other hand, the peaks with little width seen in Figure 2 denote the high crystallinity of indium oxide (In2O3), greater than 90%.
    It also reports on the size of Pd crystals, between 2 and 20 nm, being comparable to the data obtained with other techniques such as TEM.
    20 The catalyst obtained has a BET area of 2 m2 / g and an average pore size of 142 Å.
    Example 3. Synthesis of a supported Pd / In2O3 catalyst in Al2O3 spheres
    The palladium (Pd) catalyst is synthesized using 1 mm aluminum oxide (Al2O3) spheres as support.
    Indium oxide (In2O3) was incorporated into the support by impregnation in excess of
    30 solvent, using a rotary evaporator to evaporate the water and ensure homogeneity. The precursor salt of indium oxide (In2O3) was indium nitrate (In (NO3) 3) dissolved in water (1 gram of salt per gram of spheres). A volume of 20 ml per gram of spheres was used. After impregnation, the resulting material was dried for 17 hours at 100 ° C and calcined at 500 ° C for 2 h in air.


    Palladium (Pd) was incorporated into the support (In2O3 / alumina) by impregnation in excess, reaching 5% palladium (Pd) by weight. The precursor palladium salt used was palladium chloride (PdCl2) dissolved in water. A volume of 2 ml of this solution per gram of In2O3 / Al2O3 was used. After impregnation, the material
    The resulting was dried for 17 hours at 100 ° C and calcined at 500 ° C for 2 h inair.
    Optionally, the catalyst can be reduced to 100 ° C under a hydrogen atmosphere (H2) or at room temperature for one hour before use.
    The catalyst obtained is physically and chemically stable, maintaining high stability for 300 hours in catalytic tests after resistance tests in aqueous and organic media in an ultrasonic bath for one hour, as shown in Figure 3.
    15 The conditions under which this stability study was carried out correspond to a temperature of 25 ºC and 1 atm of pressure, QH2O = 0.4 mL / min QH2 = 0.75 mL / min, QCO2 = 0.75 mL / min, [NO3 -] = 100 mg / L, and 0.3 g of catalyst.
    20 The catalyst obtained has a BET area of 100 m2 / g and an average pore size of 87 Å.
    Example 4. Nitrate removal (NO3-) with Pd / SnO2 and Pd / In2O3 catalysts
    The catalytic test was carried out in a stirred tank reactor of 0.5 L capacity, with magnetic stirring (700 rpm). 0.25 L of an aqueous nitrate solution (NO3-) (100 mg / L) was added as the reaction medium to which the Pd / SnO2 catalyst or Pd / In2O3 synthesized according to Examples 1 was added and 2 in a concentration of 1 g / L. The reaction medium was adjusted to acidic pH between 5 and
    30 6 feeding carbon dioxide (CO2) with a flow rate of 8 mLN / min. The catalytic reaction began by adding hydrogen (H2) to the reactor (flow rate = 15 mLN / min, at 25 ° C and atmospheric pressure). The results are shown in Figure 4.
    Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry to


    determine the concentration of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +) in the reaction medium.
    It can be seen that the results obtained with the Pd / In2O3 catalyst
    5 synthesized according to Examples 1 and 2 are manifestly better atobtained by using Pd / SnO2 as support in terms of activity and selectivity ofammonium (NH4 +). The nitrite concentration (NO2-) observed when adding carbon dioxideCarbon (CO2) is negligible.
    10 Example 5. Nitrate removal (NO3-) with Pd / In2O3 catalyst without and with pH adjustment
    The catalytic test was carried out in a stirred tank reactor of 0.5 L capacity, with magnetic stirring (700 rpm). It was used as a reaction medium
    0.25 L of an aqueous solution of nitrate (NO3-) (100 mg / L) to which the Pd / In2O3 catalyst (1 g / L) synthesized according to Example 2 was added. The reaction medium it was adjusted to acidic pH between 5 and 6 by feeding carbon dioxide (CO2) with a flow rate of 8 mLN / min. The catalytic reaction began by adding hydrogen (H2) to the reactor (flow rate = 8 mLN / min, at 25 ° C and atmospheric pressure). The results are
    20 shown in Figure 5.
    Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry to determine the concentration of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +) in the
    25 medium
    It can be seen how the selectivity to ammonium (NH4 +) decreases when a stream of carbon dioxide (CO2) is used in the medium for pH adjustment. The nitrite concentration (NO2-) observed when adding carbon dioxide (CO2) is
    30 despicable.
    Example 6. Elimination of nitrate (NO3-) with the catalyst Pd / In2O3 by feeding a low flow rate of hydrogen (H2) and with pH adjustment
    35 The catalytic tests were carried out in a stirred tank reactor of 0.5 L capacity, with magnetic stirring (700 rpm). It was used as a reaction medium


    0.25 L of an aqueous nitrate solution (NO3-) (100 mg / L) to which the Pd / In2O3 catalyst (1 g / L) synthesized according to Example 2 was added. The reaction medium was adjusted to acidic pH between 5 and 6 by feeding carbon dioxide (CO2) at a flow rate of 8 mlN / min. The catalytic reaction began by adding hydrogen (H2) to the
    5 reactor (flow rate = 0.3; 8.0 mLN / min, at 25 ° C and atmospheric pressure). The results areshown in Figure 6.
    Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry to
    10 determine the concentration of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +) in the medium.
    Under these operating conditions, concentrations of ammonium (NH4 +) below 0.5 mg / L at 50% conversion of nitrate (NO3-) are achieved, thus complying
    15 the legal requirements of the European Union for nitrate (NO3-) and ammonium (NH4 +) for a water to be treated containing 100 mg / L nitrate (NO3-). The nitrite concentration (NO2-) measured under these conditions is negligible.
    Example 7. Decomposition of hydrogen peroxide (H2O2) with 20 Pd / In2O3 catalysts.
    In order to check the decomposition of hydrogen peroxide (H2O2) on the catalyst, a catalytic test was carried out under ambient conditions. For the catalytic test, a stirred tank reactor of 0.5 L capacity was used, with magnetic stirring (700 rpm) at 25 ° C and 1 atm. A volume of 0.2 L of an aqueous solution of hydrogen peroxide (H2O2) (500 mg / L) was used without pH adjustment, to which the Pd / In2O3 catalyst (0.5 g / L) was added synthesized according to Example
    1. The results are shown in Figure 7.
    30 Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry at 410 nm using the Eisenberg colorimetric method to determine the concentration of hydrogen peroxide (H2O2) in the medium. As can be seen in Figure 6, a complete conversion is achieved after one hour of reaction.


    Example 8. Comparative example of the catalytic activity of palladium (Pd-In) catalysts on aluminum oxide (Al2O3) or silicon oxide (SiO2) and palladium (Pd) on tin oxide (SnO2) and palladium (Pd) ) on indium oxide (In2O3).
    5 The catalytic test was carried out in a stirred tank reactor of 0.5 L capacity, with magnetic stirring (700 rpm). 0.25 L of an aqueous nitrate solution (NO3-) (100 mg / L) was used as the reaction medium to which different catalysts were added at a concentration of 1 g / L. The catalysts compared were Pd-In / SiO2, Pd-In / Al2O3, Pd / SnO2 or Pd / In2O3, the latter synthesized
    10 according to Example 2. All the synthesized catalysts incorporated 5% palladium (Pd) by weight, in addition the Pd-In / SiO2, Pd-In / Al2O3 catalysts had 1.25% indium (In). The Pd / SnO2 catalyst was synthesized under the same conditions as in Example 2 by replacing indium oxide (In2O3) with tin oxide (SnO2) as a powder. The other two catalysts were synthesized
    15 by adding co-impregnation with InCl2 and SnCl4 to sodium tetrachloropalate (Na2PdCl4) by impregnating the support of SiO2 or Al2O3.
    The pH of the reaction medium was not adjusted in these tests. The catalytic reaction began by adding hydrogen (H2) to the reactor (flow rate = 15 mLN / min, at 25 ° C and pressure
    Atmospheric 20). The results are shown in Figure 8.
    Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry to determine the concentration of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +) in the
    25 medium
    It can be seen that the results obtained with the Pd / In2O3 catalyst synthesized according to Example 2 are manifestly better than those obtained when using Pd / SnO2 as a support in terms of ammonium activity and selectivity
    30 (NH4 +). The amount of ammonium (NH4 +) generated with the Pd / In2O3 catalyst was 50% lower than that generated with the other three catalysts (Figure 8).


    Example 9. Comparative example of the catalytic activity of palladium (Pd) catalysts on indium oxide (In2O3) with and without prior calcination.
    This example tries to compare two synthesized catalysts as described
    5 in Example 1 with the only difference that in one of them theprevious calcination stage. The catalysts compared were both Pd / In2O3.The catalytic test was carried out in a stirred tank reactor of 0.5 L ofcapacity, with magnetic stirring (700 rpm). It was used as a reaction mediuman aqueous solution of nitrate (NO3-) (100 mg / L) of 0.25 L volume at which
    10 added both catalysts in a concentration of 1 g / L. Both synthesized catalysts incorporated 5% palladium (Pd) by weight following the procedure described in Example 1. The only fundamental difference between both catalysts is the calcination process that has not been used in one of the cases.
    15 The pH of the reaction medium was not adjusted in these tests. The catalytic reaction began by adding hydrogen (H2) to the reactor (H2 flow rate = 8 mLN / min, at 25 ° C and atmospheric pressure) and carbon dioxide (CO2) (CO2 flow rate = 8 mLN / min, at 25 ° C and atmospheric pressure ). The results are shown in Figure 9.
    20 Samples taken periodically and filtered by regenerated cellulose filters (0.45 µm pore) were analyzed by spectrophotometry to determine the concentration of nitrate (NO3-), nitrite (NO2-) and ammonium (NH4 +) in the medium.
    25 It can be seen that the results obtained with the Pd / In2O3 catalyst synthesized according to Example 1 with prior calcination are remarkably better after 3 h of test than those obtained with the uncalcined catalyst in terms of catalytic activity and ammonium selectivity (NH4 + ). As soon as a conversion of nitrate (NO3-) of 25% was observed with the catalyst without prior calcination
    30 compared to 100% nitrate conversion (NO3-) obtained with the catalyst with prior calcination. Lower ammonium (NH4 +) production values are observed in the case of the catalyst with prior calcination (Figure 9).
    As can be seen in this example, with the calcination stage,
    35 achieves a better distribution of the metal over indium oxide (In2O3). The calcination of the material allows to form a proportion of active nanoparticles of


    Palladium (Pd) on indium oxide (In2O3) that are not achieved in the case of a calcination step where the palladium salt remains precipitated on its surface in the uncalcined catalyst.
    5 Example 10. Comparative example of the morphology between palladium (Pd) nanoparticles on indium oxide (In2O3) in palladium (Pd) catalysts on indium oxide (In2O3) with and without prior calcination.
    This example attempts to compare two catalysts, the first as described in Example 1 and the second corresponds to the catalyst previously described by N.
    S. Smirnova et al., Chemistry for Sustainable Development, 2013, 21, 91-100.
    Figures 10 and 11 show how the palladium (Pd) nanoparticles in the support synthesized on indium oxide (In2O3) have a spherical morphology with 15 nanoparticle sizes between 2 and 10 nm (approximately 5 nm) uncoated. That is, indium oxide (In2O3) films on the surface of palladium (Pd) are not appreciated, which avoids the problems found in the prior art related to this indium oxide (In2O3) film and prevents the passage of the reactants to the noble metal so that it affects a lower speed of
    20 partial or total reaction or inactivation of the noble metal function depending on the degree of coating.

    权利要求:
    Claims (32)
    [1]
    1. A catalyst comprising a noble metal of group VIIIB of the Periodic System of the Elements in the form of spherical monometallic nanoparticles
    5 of a size between 2 and 20 nm uncoated, found inDirect contact with an indium oxide surface that acts as a support.
    [2]
    2. Catalyst according to claim 1 wherein the noble metal is selected from palladium, rhodium, ruthenium, platinum, iridium, in its zero-valent state, in any of
    10 its most stable oxidation states, or in any of the possible combinations.
    [3]
    3. Catalyst according to claims 1 to 2 wherein the noble metal is palladium.
    4. Catalyst according to claims 1 to 3 wherein the proportion of noble metal incorporated into the catalyst is between 0.1% and 30% by weight with respect to the weight of the catalyst.
    [5]
    5. Catalyst according to claims 1 to 4 wherein indium oxide can be used both in its crystalline and amorphous form.
    [6]
    6. Catalyst according to claims 1 to 5 wherein the catalyst is supported.
    [7]
    7. Catalyst according to claim 6 wherein the supports are selected from
    25 alumina, silica gel, zeolites, clays, cordierite ceramic monoliths, iron / chromium / alumina alloys, ceramic or polymeric membranes, ceramic, metal or polymeric extrudates.
    [8]
    8. Process for obtaining the catalyst described according to claims 1 to 30 7, comprising the following steps:
    (to) incorporation of the noble metal on indium oxide;
    (b) drying of the product obtained in step (a) at a temperature between 25 ° C and 200 ° C;
    (c) calcination between 200 ° C and 600 ° C of the product obtained in step (b). 35
    [9]
    9. The method according to claim 8 wherein optionally a subsequent step of activating the product obtained in step (c) is carried out by means of the

    application of hydrogen at a temperature from 25 ° C to 250 ° C, preferably between 25 ° C and 120 ° C.
    [10]
    10. Method according to any of claims 8 and 9 wherein the noble metal
    5 of group VIIIB of the Periodic System of Elements used in step (a)select from palladium, rhodium, ruthenium, platinum, iridium, in any of itsoxidation states, or any of the possible combinations.
    [11]
    11. Method according to claim 10 wherein the noble metal is palladium or its
    10 precursor salts that are selected from palladium chloride, palladium nitrate, sodium tetrachlorolate (II), palladium acetate, palladium tetramin nitrate and palladium hexafluoride acetylacetonate.
    [12]
    12. Method according to any of claims 8 to 11 wherein the
    The incorporation of the noble metal onto indium oxide in step (a) is carried out by methods comprising wet impregnation, impregnation to incipient moisture, precipitation-deposition, chemical vapor deposition from metalorganic compounds or chemical deposition. in vapor phase.
    13. A method according to claim 12 wherein the methods of step (a) employ aqueous or organic solutions selected from methanol, ethanol and acetone, and any of their mixtures.
    [14]
    14. Method according to any of claims 8 to 13 wherein the product
    25 obtained in step (a) may be supported and this support may be incorporated before or after step (a).
    [15]
    15. Method according to claim 14 wherein the support is incorporated before
    step (a) starting from supported indium oxide. 30
    [16]
    16. Method according to claim 14 wherein the product obtained in the step
    (a) is incorporated on a support before carrying out step (b).
    [17]
    17. Method according to claims 14 to 16 wherein the supports are
    35 select from alumina, silica gel, zeolites, clays, cordierite ceramic monoliths, iron / chromium / alumina alloys, ceramic or polymeric membranes, ceramic, metal or polymeric extrudates.

    [18]
    18. Use of a catalyst according to any of claims 1 to 7 for the removal of contaminants in water.
    [19]
    19. Use according to claim 18, wherein the contaminants are selected from nitrate, nitrite, halogenated compounds, heavy metals and peroxides.
    [20]
    twenty. Use according to claim 19, wherein the contaminant is nitrate.
    [21]
    twenty-one. Use according to claim 19, wherein the halogenated compounds are selected from perchlorate, chlorate and chlorite.
    [22]
    22 Use according to claims 18 to 21 wherein the purification of contaminated water is carried out by removing the contaminants by catalytic reduction reactions, hydrodehalogenation or both simultaneously.
    [23]
    2. 3. Process for purification of contaminated water comprising contacting the catalyst described according to any one of claims 1 to 7 with the stream of water to be treated.
    [24]
    24. Process according to claim 23 wherein the catalyst is in a reactor selected from a fixed bed reactor, fluidized bed reactor, catalytic membrane reactor and monolithic reactor.
    [25]
    25. Process according to any one of claims 23 to 25 wherein the purification of the contaminated water consists in the removal of the contaminants by catalytic reduction reactions, hydrodehalogenation or both simultaneously.
    [26]
    26. Process according to claim 25 wherein the catalytic reduction comprises saturation of the water to be treated with a reducing agent before or after the catalyst is brought into contact with the water stream to be treated.
    [27]
    27. Process according to claim 26 wherein the reducing agent is hydrogen gas.
    [28]
    28. Process according to claim 26 wherein the reducing agent is formic acid or hydrazine.

    [29]
    29. The method according to claims 26 to 28 wherein the reaction temperature is between 5 ° C and 90 ° C, the gas pressure is between 1 bar and 10 bar and the pH of the medium is between 3 and 7.
    [30]
    30. Method according to claim 29 wherein the pH of the medium is between 4.5 and
    [6]
    6.
    [31]
    31. Method according to any of claims 23 to 30, wherein
    10 contaminants are selected from nitrate, nitrite, halogenated compounds, heavy metals and peroxides.
    [32]
    32. Method according to claim 31 wherein the contaminant is nitrate.
    A method according to claim 31 wherein the halogenated compounds are selected from perchlorate, chlorate and chlorite.
    [34]
    34. A method according to claim 32 wherein the removal of nitrate is carried out by catalytic reduction where the amount of hydrogen is limited to
    20 partial pressures lower than 0.05 or dissolved hydrogen concentrations lower than 0.2 mg / l and the reaction temperature is between 5 ° C to 25 ° C.

    FIG. one
    FIG. 2

    FIG. 3
    FIG. 4

    FIG. 5
    FIG. 6

    FIG. 7
    FIG. 8

    FIG. 9
    FIG. 10

    FIG. eleven
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    AR092519A1|2013-09-11|2015-04-22|Univ Nac Del Litoral|CATALYTIC PROCESS FOR THE POTABILIZATION OF WATERS CONTAMINATED WITH NITRATES|
    KR101547100B1|2014-02-12|2015-08-25|한국과학기술원|Bimetallic catalyst for high nitrate reduction and selectivity and Manufacturing method thereof|
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