Bimetallic Pd-Pt/HY catalysts prepared by the co-impregnation method with an atomic variation of Pd/Pd+Pt were studied to convert toluene and methylcyclohexane. The catalysts were characterized by the BET method, chemisorption of CO by the pulse method, programmed temperature reduction (H2-TPR), and programmed ammonia thermo-desorption (NH3TPD). Results of chemisorption of CO and H2-TPR for Pd-Pt/HY catalysts suggest the existence of a strong interaction between Pd and Pt. The NH3-TPD showed that incorporating metals influences the percentage of relative distribution of weak/strong acid sites presented in decreasing order of acidity: Pd0Pt100/HY>Pd100Pt0/HY>Pd33Pt67/HY. Atomic composition Pd/Pd+Pt equal to 0.33, and relative distribution of weak/strong acid sites equal to 2, favor hydrogenation of toluene to methylcyclohexane in metal sites and subsequent skeletal isomerization in the acidic sites through dimethylcyclopentane intermediate and ring-opening in the metal sites, leading to increased formation of n-heptane relative to iso-heptane. Bimetallic Pd-Pt/HY catalysts prepared by the co-impregnation method with an atomic variation of Pd/Pd+Pt were studied to convert toluene and methylcyclohexane. The catalysts were characterized by the BET method, chemisorption of CO by the pulse method, programmed temperature reduction (H2-TPR), and programmed ammonia thermo-desorption (NH3TPD). Results of chemisorption of CO and H2-TPR for Pd-Pt/HY catalysts suggest the existence of a strong interaction between Pd and Pt. The NH3-TPD showed that incorporating metals influences the percentage of relative distribution of weak/strong acid sites presented in decreasing order of acidity: Pd0Pt100/HY>Pd100Pt0/HY>Pd33Pt67/HY. Atomic composition Pd/Pd+Pt equal to 0.33, and relative distribution of weak/strong acid sites equal to 2, favor hydrogenation of toluene to methylcyclohexane in metal sites and subsequent skeletal isomerization in the acidic sites through dimethylcyclopentane intermediate and ring-opening in the metal sites, leading to increased formation of n-heptane relative to iso-heptane.

The purpose of this study was the preparation of Pt and Pt–Sn catalysts supported on a HY zeolite (Si/Al=3) induced by microwave radiation as heating source. The solids were characterized by means of X-ray diffraction (XRD), elemental chemical analysis, nitrogen physisorption at −196°C, and X-ray photoelectron spectroscopy (XPS). Catalytic activity of the solids was evaluated using the toluene hydrogenation reaction. The XRD analysis showed that the zeolite structure was maintained after metal deposition. XPS revealed the presence of Pt0 species in monometallic catalyst, while in bimetallic Pt–Sn catalysts, Pt0 and SnOx species were found, which seem to be strongly interacting. The toluene hydrogenation reaction showed a drastic decrease in activity for bimetallic Pt–Sn catalyst, which was attributed to either a geometric and/or electronic interaction taking place on the Pt sites and tin species, avoiding, toluene adsorption.

Silver nanoparticles (AgNPs) were prepared by means of the polyol method in the absence of stabilizing polymers. To accomplish this objective, AgNO3 was added to ethylene glycol in the presence of NaOH (1 mol.L-1), the suspension formed was irradiated with a microwave source for 60 seconds at a power of 465 watts. It was found that under these conditions AgNPs of sizes between 4-18 nm are formed. Also the results indicate that part of the ethylene glycol is oxidized to carbonyl compounds that reduce the Ag+. These organic compounds are adsorbed on the surfaces of AgNPs, forming a protective film that prevents their aggregation.

Se presenta un estudio sobre la preparacion de aluminas porosas utilizando un medio acuoso y como agentes orientadores de la estructura diferentes tipos de carbohidratos (glucosa, lactosa y almidon), las cuales son sustancias de bajo costo y de alta disponibilidad comercial. El tratamiento de secado de la mezcla se realizo a una temperatura de 388 K y la calcinacion se efectuo a 873 K, lo que permitio sintetizar la fase gamma de las aluminas. Los productos obtenidos presentan caracteristicas texturales interesantes para su potencial aplicacion en catalisis heterogenea y fenomenos de adsorcion: areas superficiales (metodo BET) alrededor de 300 m2/g, volumen total de poros del orden de 0,40 cm3/g y estrechas distribuciones de tamanos de poro (metodo BJH), los cuales estan alrededor de 6,5 nm. Los solidos obtenidos fueron caracterizados mediante varias tecnicas, tales como fisisorcion de N2, DRX, MEB, IRFT, ello permitio demostrar que dependiendo del agente templante utilizado, se obtienen materiales con diferentes propiedades texturales, lo que pudiera deberse a la manera como interactuan el agente orientador y las especies de aluminio.

Three H-ZSM5 solids with Si/Al atomic ratios of 22, 71 and 96 were synthesized and characterized by X-ray diffraction (XRD), ICP-AES chemical analysis and nitrogen physisorption at −196°C. These were employed as supports in the synthesis of Pt/H-ZSM5 catalysts with platinum contents around 1wt.%, by means of the microwave-assisted polyol method: platinum salt solutions in ethylene glycol were irradiated at powers of 184 and 461W for time periods of 30 and 60s in order to obtain Pt nanoparticles suspensions which were mixed with the supports and ultrasonically irradiated for 30min to obtain the catalysts. This methodology allowed the synthesis of the catalysts efficiently and in relatively short times. Characterization of the catalysts by XRD showed that the ultrasonic irradiation did not affect the support structure. X-ray photoelectron spectroscopy revealed the presence of Pt(0) species on the solids surfaces. Temperature-programmed reduction studies suggested an effect of the time and power of microwave irradiation on the reducibility of the catalysts, i.e., at the shorter times and lower irradiation powers, the reducibility of the platinum species decreases. Catalytic testing through the hydrogenation of toluene indicated that there is an effect of time and power of microwave irradiation on the initial hydrogenation activity of the Pt/H-ZSM5 catalysts. The catalyst prepared from suspensions irradiated at 461W for 60s showed the highest activity, which seems to be related to the lower particle size and better dispersion of Pt.

This work presents the preparation and characterization of three bifunctional catalysts consisting of palladium supported on H-[Ga]ZSM5 zeolite, with a Si/Ga atomic ratio of 16 and Pd contents of 0.09, 0.50 and 1.02wt%. The lowest and highest Pd content solids, which were assessed by transmission electron microscopy (TEM), show dispersion of the supported phase of 90% and 73%, respectively. The XPS characterization studies of the catalysts allowed to detect the presence of framework, tetrahedral Ga species, Pd(0) aggregates and Pd(0) atomically dispersed. These solids were tested in the synthesis of methyl isobutyl ketone (MIBK) from acetone. The results confirm that the catalyst with 1.02wt% Pd, shows an initial global activity about twice as higher as that of 0.09wt%Pd/H-[Ga]ZSM5, and additionally the selectivity to MIBK of the former is four times higher. These results show that the catalyst with lower Pd content do not have a high number of active metallic sites to catalyze the hydrogenation of Mesityl oxide to MIBK, even though it showed an excellent dispersion, while the catalyst with 1.02wt% Pd seems to be a catalyst with a proper balance of the acidic-hydrogenating functions.

Solids of the MCM-41 type (BET specific surface area around 600m2/g), with only Si and with Si/Al (atomic ratio)=25, were synthesized and employed as supports of dodecatungstophosphoric acid (HPW)-based catalysts. Catalysts were prepared by impregnation of HPW, in amounts of 20, 40 and 60wt%. Characterization by DTA, TGA, XRD, FT-IR and NH3-TPD suggest an interaction of HPW with the supports. This interaction in the HPW/MCM-41 (Si) catalysts leads to a higher thermal stability of the Keggin structure of HPW and thus a preservation of its acidic protons. This effect is reflected in a higher density of acid sites upon increasing HPW loading. Powder XRD patterns of catalysts and the steady loss of specific surface area in both supports are consistent with a uniform distribution of the supported HPW. Analysis by FT-IR of the supported catalysts shows a displacement of the W–O–W band of supported HPW as compared with pure HPW. This displacement decreases with increasing loading, being higher for 20% HPW/(Si/Al). The catalytic activity in the alkylation of toluene with 1-dodecene increases in the following sequence: 20% HPW/(Si/Al)<40% HPW/(Si/Al)<20% HPW/(Si)<60% HPW/(Si/Al)<40% HPW/(Si)<60% HPW/(Si), which is directly related to the acid site density. The conversions and selectivities towards monoalkylated products for HPW/MCM-41 (Si) catalysts are higher than those for HPW/MCM-41 (Si/Al). The 60% HPW/MCM-41 (Si) catalysts presents the higher selectivity to monoalkylated products and the higher thermal stability, while for 20% HPW/MCM-41 (Si/Al) no catalytic activity was observed.

An MFI type galosilicate was synthesized and characterized employing XRD, N2 adsorption at −196°C, chemical analysis by ICP-AES, and XPS. This material was used in the preparation of Pd/H[Ga]ZSM5 and Pt/H[Ga]ZSM5 bifunctional catalysts, calcined under dry air for 6h at 500 and 300°C, respectively, and then reduced “in situ” under H2 flow for 6h at 500°C. The bifunctional catalysts were also characterized by XRD, N2 physisorption, TEM, chemical analysis, and XPS. The support possesses an MFI structure with excellent crystallinity, as shown by XRD. Bulk chemical analysis shows a (Si/Ga)ICP-AES atomic ratio of 16. The absence of Ga2O3 is suggested by both XRD and XPS (at surface level). The atomic ratio at the surface, (Si/Ga)XPS, is the same as that found by ICP-AES, suggesting that Ga is distributed homogeneously. XRD and N2 physisorption results of the bifunctional catalysts suggest that metal incorporation does not affect sensibly the structure of the support. Dispersion of Pd and Pt in either catalyst was estimated from TEM analysis, indicating in both cases values of the order of 80%. The atomic ratios (Si/Ga)XPS at the surface were 16 for Pd/Galosilicate, and 4 for Pt/Galosilicate, suggesting that Pt promotes migration of Ga towards the external surface of the solid, a phenomenon that is not observed for the Pd/H[Ga]ZSM5 catalyst. Degaliation promoted by Pt could be explained assuming that Pt and Ga could form stable chemical species, as might be indicated by XPS results. The transformation of acetone to MIBK was employed as catalytic test. These results indicate very different behaviors for either bifunctional catalyst.

The purpose of this work is to elucidate the effect of acid sites density on the catalytic behaviour of a series of bifunctional catalysts prepared by supporting platinum (about 1.00wt.%) on MFI-type gallosilicates (H[Ga]/ZSM5 with Si/Ga atomic ratio=16, 46 and 145). The XPS characterization studies of the bifunctional catalysts allowed to detect the presence of framework as well as extraframework gallium species for the catalyst with highest density of acid sites (Si/Ga=16), while only framework Ga species could be detected for catalysts with lower acid site density. It was also verified in all the bifunctional catalysts the presence of three types of metal sites: Pt (0), Pt–Oads and PtO species. The results obtained in the synthesis of MIBK from acetone with the different bifunctional solids, indicate that as the density of the acid sites increases, the solids start to behave solely as acid catalysts. This phenomenon is probably related to the presence of extraframework gallium species in the catalyst with higher surface acidity, capable to interact with the platinum species and thus provoking the passivation of the metallic phase, while in the solids with lower surface acidity it seems to exist a better balance between the acidic–metallic functionalities.

Removal of nitrates and nitrites from drinking water by catalytic hydrogenation over zeolite-supported Pt–Sn catalysts was studied. Bimetallic Pt–Sn/HZSM-5 catalysts were characterized by temperature-programmed reduction (TPR), H2 chemisorption, X-ray photoelectron spectroscopy (XPS) and 119Sn Mössbauer spectroscopy. The characterization techniques showed a significant decrease in the H/Pt ratio upon tin addition, tin surface enrichment, the formation of PtSn alloys and platinum catalysis of the tin reduction. The Pt–Sn/HZSM-5 catalyst clearly showed high catalytic activity for the reduction of nitrate to form N2. In the bimetallic catalyst, the role of tin is to reduce nitrate or nitrite according to a redox process, while the platinum maintains tin in the metallic state.

Bifunctional monometallic Pt/H[Al]ZSM5, Sn/H[Al]ZSM5 and bimetallic PtSn/H[Al]ZSM5 catalysts were prepared and characterized by means of XPS, TEM and toluene hydrogenation. For the bimetallic samples, co-impregnation of both metals and sequential impregnation (where Sn was added to monometallic Pt catalysts) were used with two tin atomic fractions, XSn=0.46 and 0.28. Based on XPS data, it was found that the surface composition of the Pt–Sn bimetallic catalysts depends on the impregnation method employed: in the co-impregnated samples alloys form between both metals, while in the sequentially impregnated catalysts no alloy formation occurs but both Pt and Sn are easily reduced. Also, TEM analysis showed that the co-impregnated samples have similar particle sizes as the monometallic Pt catalysts, but that the particles in the sequentially impregnated samples are of larger sizes, closer to those seen in monometallic Sn catalysts. It is suggested here that while in the former case the particle size is not affected by the formation of Pt–Sn alloys, in the latter the tin covers the Pt species, and therefore increases the overall particle size. Finally, it was found that some hydrogenating activity could be detected with the co-impregnated catalysts but not with the sequentially impregnated samples, even though the latter had only a small fraction of atomic tin. In general, the results obtained in this study show a significant variation in catalytic properties with the method of preparation used for these bifunctional PtSn/H[Al]ZSM5 catalysts.

The purpose of this work is to elucidate how platinum supported on a gallosilicate of the MFI type interacts with extra-framework and/or framework gallium, thus affecting the properties of bifunctional catalysts of the Pt/H[Ga]MFI type. To this end, a gallosilicate and an aluminosilicate of the MFI type, with a Si/M atomic ratio≅15 (M=Ga, Al) were synthesized and characterized by X-ray diffraction (XRD), nitrogen physical adsorption at −196°C, and chemical analysis by ICP-AES. These zeolites were used as supports in the preparation of a series of bifunctional catalysts with varying Pt content: 0.10wt.% Pt/H[Ga]ZSM5, 0.50wt.% Pt/H[Ga]ZSM5, 1.00wt.% Pt/H[Ga]ZSM5 and 1.00wt.% Pt/H[Al]ZSM5, which were assessed by transmission electronic microscopy (TEM); dispersion of the supported phase was found to range within 50 and 80%. The supports (gallosilicate and aluminosilicate) as well as the bifunctional catalysts were characterized by X-ray photoelectron spectroscopy (XPS) to determine the chemical species on their surfaces. The presence of extra-structural gallium was observed in Pt/H[Ga]ZSM5, which could be found most probably as Ga2O3; the presence of Pt0, Pt–Oads, and PtO in Pt/H[Ga]ZSM5 and Pt/H[Al]ZSM5 was also observed. It was also evidenced an increase in surface gallium concentration as the content of platinum increases in the Pt/H[Ga]ZSM5 solids. The bifunctional catalysts were catalytically tested under standard conditions by the acetone transformation reaction. The results of the catalytic test confirms that the 1.00wt.% Pt/H[Al]MFI catalyst shows an initial global activity four times higher than the 1.00wt.% Pt/H[Ga]MFI one, and additionally a selectivity to the desired product (methyl isobutyl ketone, MIBK), three times higher. The activity and selectivity results observed for the Pt/H[Ga]MFI solids are remarkably similar to those found for the pure H[Ga]ZSM5 support. These results clearly show that the platinum metallic centers on the Pt/H[Ga]ZSM5 catalysts are not active for the hydrogenation reactions of the olefinic and/or carbonylic double bonds, probably due to passivation caused by the gallium species on the surface of the bifunctional catalysts.

The aim of this work is to find out how platinum supported over a gallosilicate of the MFI type influences the removal of Ga from the framework and affects the properties of the Pt/H[Ga]ZSM5 catalysts. In this regard, a gallosilicate and an aluminosilicate of MFI structure, with a Si/M ratio ≈15 (M = Ga, Al) were synthesized and characterized by XRD, nitrogen physical adsorption at −196 °C and chemical analysis by ICP-AES. Afterwards, they were used to prepare the following bifunctional catalysts: xPt/H[Ga]ZSM5 (x=0.10, 0.50 and 1.00 wt.% Pt) and 1.00%Pt/H[Al]ZSM5, which were characterized by ICP-AES, TEM, XPS, and the model reaction of toluene hydrogenation. The results found show dispersions within 50–80% for the supported platinum; the XPS analysis indicated a decrease in the Si/Ga ratio as a response to the increase of Pt content, suggesting a substantial influence of platinum on the migration of structural Ga toward the surface of the catalysts. This nonframework gallium remains oxidic and appears to strongly interact with Pt, which considerably affects the hydrogenating ability of these catalysts.

A study was carried out on the reaction of acetone transformation over bifunctional monometallic (Pt/H[Al]ZSM5, Sn/H[Al]ZSM5) and bimetallic (PtSn/H[Al]ZSM5) catalysts with variation of their tin atomic fraction (XSn=number of Sn moles/number of Sn moles + number of Pt moles). The solids prepared were analyzed by means of X-ray diffraction (XRD), nitrogen adsorption at −196°C, chemical analysis through inductive coupled plasma–atomic emission spectroscopy (ICP–AES) technique, energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electronic paramagnetic resonance (EPR), transmission electronic microscopy (TEM), and by means of test reaction of toluene hydrogenation. Acetone transformation was carried out at 160°C, under atmosphere pressure, at an acetone/hydrogen molar ratio of 3 and varying WHSV. The results obtained show a sensitive variation in the catalytic properties as XSn is varied in the series of PtSn/H[Al]ZSM5 catalysts prepared; these changes are attributed to the presence of effects of the electronic and geometric type, which would be a consequence of the formation of a Pt–Sn alloy and probably of the phenomenon of decoration of platinum particles, which is evidenced from the evaluation of the solids by means of XPS and EPR.

A series of bifunctional bimetallic PtCu/H[Al]ZSM5-type catalysts was prepared and acetone transformation was carried out over them at 160 °C, 1 atm, acetone/hydrogen molar ratio=3, and WHSV (weight of reactant injected per weight of catalyst per hour) ranging between 9.4 and 38 h −1 . According to the results, as copper atomic fraction ( X (Cu)) increases in the bimetallic catalyst, propane formation rate decreases and methyl isobutyl ketone (MIBK) formation rate increases until X (Cu) equals 0.40. These results suggest that active metallic centers for the olefin double bond hydrogenation in the α-β unsaturated ketone, which leads to the MIBK formation, do not appear to be those hydrogenating the acetone carbonyl double bond to form propane. When X (Cu)>0.40, MIBK formation rate considerably decreases, meaning that practically all platinum metallic centers have been passivated for those copper atomic fractions over the PtCu/H[Al]ZSM5-type catalyst. Therefore, catalysts begin to act only by means of the acid function, and as a result a logical increase in the mesityl oxide (MO) concentration occurs, a substance that is formed by means of an acid catalysis.

Removal of nitrates from drinking water by catalytic hydrogenation over ZSM-5 supported Pt-Cu catalysts was studied. Bimetallics Pt-Cu were prepared by ion exchange of copper on a parent monometallic platinum catalyst. Monometallic platinum catalysts are inactive for nitrate reduction, while Pt-Cu bimetallic catalysts are active for nitrate removal. In the bimetallic catalyst, the role of copper is probably to reduce nitrate according to a redox reaction. The addition of copper to Pt catalysts decreases the production of ammonium ions

The gas phase transformation of acetone, cyclohexanone and acetophenone was investigated in a fixed bed reactor over series of bifunctional Pt and Pd/molecular sieves (HFAU, HBEA, HMFI, HMCM41). Ketones resulting from three successive steps: aldolisation and dehydration of the resulting ketoalcohols on the acid sites then hydrogenation on the metallic sites can be obtained in one apparent step. Various other bifunctional transformations of the reactant, of the ketone product alone or of both can also be observed. However, the ketone products can be obtained with a high selectivity by an adequate choice of the pore structure and the adjustment of the acid and hydrogenating properties. Thus the pores of the molecular sieves should be large enough to allow an easy desorption of the ketone products and narrow enough to limit the formation of very bulky secondary compounds and of coke. Whereas for acetone transformation into methylisobutylketone an average pore size zeolite (e.g. MFI) should be used, a large pore zeolite (e.g. FAU) is preferred for cyclohexanone transformation into cyclohexylcyclohexanone and a mesoporous MCM41 silicoaluminate for acetophenone transformation into 1,3-diphenyl-butan 1-one.

Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure and acetone/H 2 molar ratio=3. The reaction was carried out over Pt/HMFI bifunctional catalysts, with 0.30 wt% of platinum which was supported over three aluminosilicates (Si/Al ratio=40, 95 and 160) and a borosilicate (Si/B ratio=44) with similar dispersion. The results show that catalytic properties depend greatly on density and strength of the acidic sites of the catalysts. Moreover, the limiting step of the MIBK synthesis reaction (aldolization of two acetone molecules) is carried out over the acidic sites of the aluminosilicates, but not over those of the borosilicate, which considerably affects reaction selectivity.