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Changes in the oxidation state and chemical environment of vanadium in poisoned and regenerated hydrotreatment (HDT) catalyst were followed by electron paramagnetic resonance (EPR). Oxovanadyltetraphenil porphyrin was used as model poison molecule on synthesized CoMo/Al2O3 HDT-UCV-1 catalyst. Unconventional methodologies of carbiding and nitriding were applied to the deactivated catalyst aiming at recovering its catalytic properties. The results showed that the vanadium incorporation method affected the metallic species on the catalyst surface, particularly the V-support interaction. This work represents an important contribution about the understanding of new phases formed in the spent catalysts after reactivation by means of nitriding and carbiding processes, which are expected to improve the catalytic HDT response.

Quantum chemistry calculations were carried out using the ONIOM2 methodology at two different levels of calculation, B3LYP for the high level and UFF for the low level. These calculations were performed on Cu/SAPO-11, NO–Cu/SAPO-11, NH3–Cu/SAPO-11 and NO + NH3–Cu/SAPO-11 to investigate the reaction pathway of the selective catalytic reduction of nitrogen oxides by ammonia in the presence of Cu/SAPO-11. NH2NO is formed, and then is decomposed into N2 and H2O over Cu/SAPO-11 for the catalytic reduction of NO in two steps. The adsorption energy ΔEads of NO, NH3 on Cu/SAPO-11 and the change of energy of the reduction reaction are presented. The energy profile of the formation of NH2NO–Cu/SAPO-H key intermediate is shown. Some relevant charges and bond indexes were calculated. On adsorbing NH3 or NO on Cu/SAPO-11 there is charge transfer to the aggregates. Vibrational frequencies of adsorbed NH3, NO and of NH2NO–Cu/SAPO-11cluster are reported. The importance of adsorbing NH3 previously to the reduction of NO is emphasized.

The γ-Al 2 O 3 -supported Anderson-type complexes (NH 4 ) 4 [NiMo 6 − x W x O 24 H 6 ]·5H 2 O (x = 0, 3 or 6) were carburized with CH 4 /H 2 (1:4) mixture (denoted by NiMo 6 − x W x -C/Al). These solid compounds have been tested in a continuous flow, fixed bed reactor for thiophene hydrodesulfurization and polychlorinated biphenyls hydrodechlorination, and in (semi-) batch reactor for dibenzothiophene selective oxidation. The specific surface area and pore volume of NiMo 6 -C/Al were greater than those of NiW 6 -C/Al and NiMo 3 W 3 -C/Al. XRD results evidenced a bulk structure typical of Mo 2 C, W 2 C, WC and NiC. FT-IR verified the absence of bands corresponding to metal oxides. Generally, the catalytic activity toward a given reaction product of NiMo 6 -C/Al was greater than those of NiW 6 -C/Al and NiMo 3 W 3 -C/Al due either to its better textural properties or to a more complete transformation of the metal phases into active ones.

The substituted and unsubstituted aromatic hydrocarbons, present in transportation fuels such as gasoline and diesel, are thought to be responsible for most of the soot particles produced during their combustion. However, the effects of the substituted alkyl groups on the aromatic hydrocarbons on their sooting tendencies, and on the physical and chemical properties of soot produced from them are not well understood. In this work, the effect of the presence of methyl groups on aromatic hydrocarbons on their sooting propensity, and on the oxidative reactivity, morphology, and chemical composition of soot generated from them in diffusion flames is studied using benzene, toluene, and m-xylene as fuels. Several experimental techniques including high resolution transmission electron microscopy and X-ray diffraction are used to identify the morphological changes in soot, whereas the elemental and thermo-gravimetric analyses, electron energy loss spectroscopy, and Fourier transform infrared spectroscopy are used to study the changes in its chemical properties and reactivity. The activation energies for soot oxidation are calculated at different conversion levels, and a trend in the reactivity of soots from benzene, toluene and m-xylene is reported. It is observed that the sizes of primary particles and graphene-like sheets, and the concentrations of aliphatics and oxygenated groups in soot particles decreased with the addition of methyl group(s) on the aromatic ring. The physicochemical changes in soot are found to support the oxidative reactivity trends.

The catalytic performance of Al2O3-supported monometallic and bimetallic catalysts in selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions was studied. Bimetallic catalysts were prepared by the coimpregnation method with the required amounts of the precursors salts [Ni(NO3)2·6H2O and Pd(NH3)4Cl2·H2O] over pellet-form γ-Al2O3 with a constant content of Pd (0.5 wt%) and varying Ni/Pd atomic ratio (0.25, 0.5, 0.75, and 1) obtaining egg-shell profiles of the active components. The catalysts were characterized by X-ray diffraction, temperature-programmed techniques, such as reduction in hydrogen and desorption of ammonia, N2 physisorption, and transmission electron microscopy. The catalytic test showed that the 1,3-butadiene was selectively hydrogenated when bimetallic catalysts were used. The addition of Ni to the Pd-based catalysts suppressed n-butane formation and increased recovery of 1-butene at medium conversion. Therefore, it was observed an improved catalytic performance of the bimetallic catalysts being highest in the case of the 1NiPd/Al2O3.

Hexagonal mesoporous MCM-41-type molecular sieve has been functionalized with (3-mercaptopropyl)trimethoxysilane and used to heterogenize two large Co(II)- and Cu(II)-complexes containing a terpyridine-based Schiff base macrocyclic ligand. First, thiol groups were linked to the siliceous surface of the mesoporous host via grafting process. Some samples were characterized by FTIR, ICP-AES, SA-XRD, N2 physisorption, 13C-MAS-NMR, XPS and EPR. This set of characterization techniques confirmed a successful functionalization process, and also confirmed that the used experimental procedure allowed the heterogenization of Co(II)- and Cu(II)-complexes inside the pores of the functionalized host, retaining the mesoporous structure. The homo- and heterogeneous catalysts were active for cyclopentene oxidation. Co@MCM(F) sample was reported in this article as the best catalyst due to its higher activity and selectivity, as well as its low loss of catalytic activity after reuse.

Multiwall carbon nanotubes (MWCNTs) were synthesized using p-xylene and FeMo/MgO catalysts prepared by two methods (co-impregnation and sol–gel). Carbon nanotubes with uniform diameters were obtained by catalytic chemical vapor deposition at 900 °C using FeMo/MgO catalyst prepared by sol–gel method. The sol–gel method resulted in a higher yield than the co-impregnation method; this was attributed to the better dispersion of the metallic nanoparticles due to the sponge-like structure. Additionally, MWCNTs with lower metals content were obtained after three steps of purification.

A new approach has been tested for the preparation of metal/Mo2C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to study the reduction and carburization processes of Cu3(MoO4)2(OH)2, α-NiMoO4 and CoMoO4·nH2O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo2C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu2+, Ni2+ and Co2+ cations inside each molybdate. The synthesized Cu/Mo2C, Ni/Mo2C and Co/Mo2C catalysts were highly active for the hydrogenation of CO2. The metal/Mo2C systems exhibited large variations in the selectivity towards methanol, methane and CnH2n+2 (n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C–O bonds. Cu/Mo2C displayed a high selectivity for CO and methanol production. Ni/Mo2C and Co/Mo2C were the most active catalysts for the activation and full decomposition of CO2, showing high selectivity for the production of methane (Ni case) and CnH2n+2 (n > 2) hydrocarbons (Co case).

Ni–Mo carbides supported on activated carbon were synthesized by carbothermal hydrogen reduction and the effect of the sulfidability on the thiophene hydrodesulfurization catalytic activity was studied. The X-ray diffraction patterns of Ni–Mo carbides showed the presence of β-Mo 2 C and NiC when the atomic ratio AR = Ni/(Ni + Mo) was between 0.25 and 0.75, while for AR = 1, it only was detected metallic Ni. The X-ray photoelectron spectroscopy results showed the distribution of different surface species in the passivated catalysts: Mo δ + (0 ≤ δ ≤ 2), Mo 4 + , Mo 6 + , Ni δ + and Ni 2 + . After sulfiding the carbides were modified in their surface and catalytic activity.

The effect of the pre-adsorption of sulfur on the hexagonal-Mo_{2}C-001 surface in the hydrodechlorination HDC reaction of chlorobenzene was studied using density functional theory DFT calculations. The results related with the coordination modes and the adsorption energies of the aromatic molecule suggest that the main effect of the sulfur incorporation into the surface is to lead towards a weaker chlorobenzene adsorption that will benefit the continuity of the catalytic cycle and therefore to avoid the carbonization and chlorination of the catalyst. The study of the HDC mechanism was also performed and two different reaction paths were considered. The calculated energy barriers indicate that both mechanisms may occur at the normal reaction temperature 350°C. These latter approaches involve new roles of the superficial sulfur as atomic or radical hydrogen scavenger for the S-Hformation and as a precursor of the σ chlorobenzene coordination, necessary for effective hydrogenation in the proposed mechanisms.

Pechini sol–gel method has been employed for the preparation of nanocrystalline La0.8Sr0.2FeO3 perovskite. The synthesis procedure was optimized by varying the calcination temperature. The results revealed the decomposition of the resin precursor and confirmed the formation of the perovskite phase starting at 600 °C with spherical morphology (

Unsupported Mo carbide and Mo nitride catalysts have been synthesized by temperature programmed synthesis, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H2-temperature programmed reduction and desorption and N2 physisorption. These solid compounds have been tested for the hydrodechlorination (HDCl) of polychlorinated biphenyls (PCBs) at 1 bar in a fixed bed reactor. The Mo carbides and the corresponding Mo nitride phases showed a catalytic activity higher than a conventional HDS catalyst consisting of alumina-supported NiMo sulfides (~35 %). Aroclor 1260 HDCl conversion results were related to spilt-over hydrogen species that were proposed to favor the hydrogenolysis of C–Cl bond on refractory phases. The original PCBs broad distribution changed almost completely to non-chlorinated biphenyl on the carbide and nitride catalysts.

Synthesis of bulk and alumina-supported, Fe-promoted W carbides and nitrides were carried out by using oxidic precursors with atomic ratios (Fe/(Fe + W)) varying from 0 to 1. These materials were prepared by temperature-programmed reaction up to 700 °C of the precursors under flow of 20 vol.% CH 4 /H 2 , for carbides, and of NH 3 for nitrides. Crystalline structure of catalysts was established by X-ray diffraction (XRD), while textural properties were determined by N 2 physisorption. Catalytic tests of thiophene hydrodesulfurization (HDS) were carried out in a fixed bed reactor at 400 °C and atmospheric pressure and monitored by FID-GC. The catalysts were activated in situ under a CS 2 /H 2 mixture at 300 °C/2 h prior to HDS. In addition, both fresh and exhausted catalysts were analyzed by elemental chemical analysis (ECA) of C, N and S. XRD results showed a main bimetallic phase Fe 2 WO 6 for supported oxidic precursors, while bulk catalysts revealed a mixture of Fe 2 WO 6 and FeWO 4 . On the other hand, for supported carbides, XRD revealed the presence of the cubic Fe 3 W 3 C mixed phase, and bulk carbides showed the presence of Fe 6 W 6 C. For supported nitrides, XRD data revealed the presence of the hexagonal FeWN 2 mixed phase for bimetallic catalysts and W 2.2 N 2 and Fe 3 N for each monometallic catalyst. In contrast, for bulk monometallic W nitride it was found that W 2 N was the monometallic crystalline phase obtained. Texture analysis showed that specific surface area of catalyst decreased with respect to alumina, when Fe and W were incorporated and this effect increased with increasing Fe content. Catalytic tests revealed that the catalyst based on W carbide had the highest activity, followed by the carbide catalyst with atomic ratio 0.1, which turned out to be more active than W-based nitride catalyst and the nitride catalyst with atomic ratio 0.1. Finally, after HDS, catalyst showed an increase in S content due to the displacement of C or N atoms by S atom during presulfurization and HDS reaction, which was corroborated with the decrease in C and N content of exhausted catalysts in comparison with the initial contents.

Activated (AS) and carboxymethylated (CMS0.24) cassava starch derivatives were studied as corrosion inhibitors for carbon steel XC35 in a 200 mgL-1 NaCl solution. They were characterized by back titration and Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical techniques were used to evaluate the inhibitive properties of starches at room temperature and the chemical composition of the protective films was determined by X-Ray Photoelectron Spectroscopy (XPS). Electrochemical measurements revealed that AS acts as mixed inhibitor, whereas CMS0.24 mainly inhibits the anodic reaction. In both cases, the protection increased with the inhibitor concentration; nevertheless, after 24 hours of immersion, the CMS0.24 loses its properties, while AS molecules still maintains them. XPS analyses show that the inhibitive films are composed of an iron oxide/hydroxide mixture in which starch molecules are incorporated. Results were explained taking into consideration the hydrophilicity and the strength of the ionic interaction of the starches with the metal surface.

The selective hydrogenation of 1,3-butadiene to 1-butene with toluene as a co solvent is studied experimentally over a NiPdCe/γ-Al2O3 catalyst. To reduce mass transfer limitations, an egg-shell catalyst is used in a fixed-bed reactor for liquid-phase hydrogenation of 1,3-butadiene at 40 °C and two pressure levels, 90 and 210 psig. Experimental results indicate that 1,3-butadiene conversion and selectivity of the hydrogenation process are improved when toluene is added. Conversion of 1,3-butadiene increases from 65% without toluene to 75% for 20% toluene concentration at 90 psig, while for 210 psig the observed increase is from 66% to 81%. The 1,3-butadiene selectivity toward 2-butenes is favored against 1-butene, always with preference for the thermodynamically stable trans-isomer. The 1-butene hydrogenation is controlled, decreasing the loss from 25% to 10% in the presence of toluene a 210 psig. It can be concluded that the toluene presence enhances the 1,3-butadiene selective hydrogenation and controls 1-butene consumption.

A series of tungsten and molybdenum catalysts supported on MCM-41 were prepared using Keggin heteropolyacids (H 3 PM 12 O 40 , M = Mo or W) as active phase sources and compared with their analogues unsupported. The physicochemical characterization was carried out by, small angle and wide angle X-ray diffraction; thermogravimetric analysis/differential scanning calorimetry; ultraviolet–visible diffuse reflectance and Fourier transform infrared spectroscopies; N 2 physisorption and potentiometric titration with N-butylamine, for determination, respectively, of the structure; thermal stabilities; integrity of heteropolyacids; textural properties and superficial acidity. The solids were tested in the thiophene hydrodesulfurization reaction at 400 °C, atmospheric pressure and weight hourly space velocity of 0.48 h −1 . In this study, it has been demonstrated the importance of supporting heteropolyacids to increase the catalytic activity. Furthermore, it was proved a correlation between surface acidity and calcination temperature with the activity and stability of these catalysts in the hydrodesulfurization reaction.

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 Pt 0 species in monometallic catalyst, while in bimetallic Pt–Sn catalysts, Pt 0 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.

Novel MoO(2)/C nano/microcomposites were prepared via a bottom-up approach by hydrothermal carbonization of a solution of glucose as a carbon precursor in the presence of polyoxometalates (POMs: phosphomolybdic acid [H(3)PMo(12)O(40)] and ammonium heptamolybdate tetrahydrate [(NH(4))(6)Mo(7)O(24)]·4H(2)O). The structural characterization by FT-IR, XRPD, SEM and TEM analyses revealed the controlled formation of hierarchical MoO(2)/C composites with different morphologies: strawberry-like, based on carbon microspheres decorated with MoO(2) nanoparticles; MoO(2)/C core-shell composites; and irregular aggregates in combination with ring-like microstructures bearing amorphous Mo species. These composites can be fine-tuned by varying reaction time, glucose/POM ratio and type of POM precursor. Subsequent transformations in the solid state through calcinations of MoO(2)/C core-shell composites in air lead to hollow nanostructured molybdenum trioxide microspheres together with nanorods and plate microcrystals or cauliflower-like composites (MoO(2)/C). In addition, the MoO(2)/C composite undergoes a morphology evolution to urchin-like composites when it is calcined under nitrogen atmosphere (MoO(2)/C-N(2)). The MoO(2)/C strawberry-like and MoO(2)/C-N(2) composites were transformed into Mo carbide and nitride supported on carbon microspheres (Mo(2)C/C, MoN/C, and MoN/C-N(2)). These phases were tested as precursors in thiophene hydrodesulphurization (HDS) at 400 °C, observing the following trend in relation to the thiophene steady-state conversion: MoN/C-N(2)MoN/CMo(2)C/CMoO(2)/C-N(2)MoO(2)/C. According to these conversion values, a direct correlation was observed between higher HDS activity and decreasing crystal size as estimated from the Scherrer equation. These results suggest that such composites represent interesting and promising precursors for HDS catalysts, where the activity and stability can be modified either by chemical or structural changes of the composites under different conditions.

MCM-41 type mesoporous materials of pure silicon and aluminosilicates (with Si/Al atomic ratios of 20 and 40) were prepared by a facile synthesis method and used to support NiMo catalysts. Characterization by XRD showed typical patterns of this type of mesoporous solids with a partial collapse of the structure on increasing Al content. In addition, signals attributed to the formation of MoO3, NiO and Al2(MoO4)3 in the transition-metal containing catalysts were observed. The 29Si-NMR-MAS spectra showed that local arrangement of the Si–O–Si bonds was regular, independently of the solid being pure or modified with Al, while the 27Al-MAS-NMR spectra of the aluminosilicates showed both structural and non-reticular species. The N2 adsorption–desorption curves showed type IV isotherms, with considerable diminution in the BET areas once the metals were incorporated. The catalytic results in thiophene hydrodesulfurization (HDS) and polychlorinated biphenyl hydrodechlorination (HDCl) revealed a considerable catalytic activity for all prepared catalysts as compared with a commercial NiMo/Al2O3 one, being highest in the case of the NiMo/Al-MCM-41(40) one for HDS, and for NiMo/Al-MCM-41(20) in HDCl. The excellent properties for HDCl can be attributed to good dispersion of Ni and Mo active phases and to the bifunctional character of the catalysts, namely, to the participation of both coordinatively unsaturated sites of the NiMoS active phase and Bronsted acid sites of the support.

A novel synthesis route was designed to obtain highly active vanadium based catalysts. Three different activated carbons were used as supports (one of them being treated with ozone). The supported catalysts were characterized by XRD, TEM, XPS and EPR. These systems were tested in hydrotreating reactions (HDS, HDN and hydrogenation). The characterization results showed well dispersed vanadium nanoparticles. However, it was evidenced that during the synthesis process, a vanadium carbide phase was produced within vanadium oxides. Reactivity studies showed that the vanadium catalysts were slightly better for HDS and hydrogenation reactions than a commercial NiMoS catalyst, but that was not the case for HDN reactions. The reduction method proposed is potentially an excellent route to synthesize more active supported vanadium carbide catalysts than the conventional TPS method. Under reaction conditions, carbide and sulfide vanadium species coexist in the catalyst; vanadium carbide sites probably remain intimately mixed with the active vanadium sulfide sites.

A Venezuelan garnierite sample from “Loma de Niquel” mine was treated with acid solutions of different concentrations. This method allowed an increase of BET surface area and a partial removal of Ni according to the acid concentration. The resulting solids were impregnated with Mo and their activity was tested in the thiophene hydrodesulfuration reaction. It was found that an increase of the surface area is positive for using garnierite sample in HDS reaction as long as the Ni removal was not excessive.

Temperature-programmed sulfiding (TPS) and temperature-programmed reduction of the sulfided catalysts (TPR-S) have been employed to evaluate Mo, Fe–Mo, Co–Mo and Ni–Mo carbide catalysts supported on activated carbon (AC). The carbides were prepared by carbothermal hydrogen reduction from co-impregnated precursors, and submitted to presulfiding prior to HDS. Samples of passivated catalysts prepared from the sulfates of Fe and Co contained variable amounts of sulfur, as shown by XPS and elemental analysis, while all samples showed increased sulfur contents after HDS. The TPS traces (up to 400 °C) of the Mo and Co–Mo samples exhibited two H2S consumption peaks, the first one starting at 100 °C and the second within the 400 °C isothermal region, located immediately after a H2S production peak centered at 400 °C for Mo and at 340 °C for Co–Mo. The Fe–Mo and Ni–Mo carbides exhibited a broad H2S consumption signal between 100 and 400 °C. The low temperature signals can be attributed to reduction of Mo(VI) oxide into Mo(V) or Mo(IV) sulfides, while the broad, higher temperature band is assigned to further reduction to the fully sulfided surface species. The TPR-S spectra showed three H2S evolution peaks, where the area of the first peak (assigned to reduction of sulfur species adsorbed on coordinatively unsaturated edge/corner sites) follows the order Co–Mo ≫ Ni–Mo ≈ Mo > Fe–Mo, which fully agrees with the order of HDS activities at steady state. Elemental analysis of the pre-sulfided AC support suggest that a large part of the sulfur consumed in sulfiding the catalysts is retained as elemental sulfur within the microporous structure of the support, although HRTEM observations confirm that MoS2-like structures are present in these samples. These results reinforce the importance of sulfided surface phases in HDS on carbides of transition metal catalysts. Transmission electron microscopy shows that activated carbon supported (M-)Mo carbide catalysts (M = Fe, Co, Ni) present MoS2-like fringes on top of bimetallic carbide crystals. Temperature-programmed techniques and elemental analysis prove that a large amount of sulfur is retained in the catalyst, likely within the slit-shaped microporous structure of the support. A good correlation was established between thiophene HDS activity at steady state and the size of a TPR peak of sulfided catalyst samples.

Time-resolved X-ray diffraction (XRD) has emerged as a powerful technique for studying the behavior of heterogeneous catalysts (metal oxides, sulfides, carbides, phosphides, zeolites, etc.) in-situ during reaction conditions. The technique can identify the active phase of a heterogeneous catalyst and how its structure changes after interacting with the reactants and products (80 K

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 1.02 wt%. 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 1.02 wt% Pd, shows an initial global activity about twice as higher as that of 0.09 wt%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 1.02 wt% 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 600 m 2 /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 60 wt%. Characterization by DTA, TGA, XRD, FT-IR and NH 3 -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.

Active catalysts for the water-gas shift (WGS, CO + H2O ? H2 + CO2) reaction were synthesized from nickel molybdates ({beta}-NiMoO4 and nH2O{center_dot}NiMoO4) as precursors, and their structural transformations were monitored using in situ time-resolved X-ray diffraction and X-ray absorption near-edge spectroscopy. In general, the nickel molybdates were not stable and underwent partial reduction in the presence of CO or CO/H2O mixtures at high temperatures. The interaction of {beta}-NiMoO4 with the WGS reactants at 500 C led to the formation of a mixture of Ni (24 nm particle size) and MoO2 (10 nm particle size). These Ni-MoO2 systems displayed good catalytic activity at 350, 400, and 500 C. At 350 and 400 C, catalytic tests revealed that the Ni-MoO2 system was much more active than isolated Ni (some activity) or isolated MoO2 (negligible activity). Thus, cooperative interactions between the admetal and oxide support were probably responsible for the high WGS activity of Ni-MoO2. In a second synthetic approach, the NiMoO4 hydrate was reduced to a mixture of metallic Ni, NiO, and amorphous molybdenum oxide by direct reaction with H2 gas at 350 C. In the first pass of the water-gas shift reaction, MoO2 appeared gradually at 500 C with amore » concurrent increase of the catalytic activity. For these catalysts, the particle size of Ni (4 nm) was much smaller than that of the MoO2 (13 nm). These systems were found to be much more active WGS catalysts than Cu-MoO2, which in turn is superior to commercial low-temperature Cu-ZnO catalysts.« less

The acidity and activity of promoted (with NiO) and unpromoted MoO3/A12O3 catalysts were studied by ammonia adsorption, titration using acid/base colour indicators, and thiophene hydrodesulphurisation. The incorporation of nickel into supported MoO3 produced significant changes in activity, which was attributed to changes in the number and strength of the acid sites. Specifically, the nickel decreased the concentration of highly acid sites and increased the number of sites with intermediate acidity in the oxide catalyst. At the same time, the nickel markedly increased the steady state catalytic activity but decreased the initial activity. Carbon and sulphur analyses, as well as acid site concentration of used catalysts, suggest that this behaviour may be associated with modifications brought about by nickel on MoS2 crystallite growth and on deactivation by carbon deposition. These suggestions are found to be consistent with other effects attributed to the promoter, such as hydrogen spill-over and p-semiconductivity.

The objective of the present work was to study the catalytic reformation of methane in presence of carbon dioxide on activated carbon-supported nickel and calcium catalysts. Results are very promising ones because they suggests that it is possible to transform methane on these catalysts by using mild reaction conditions.

Catalytic wet air oxidation (CWAO) of aqueous solutions of phenol, 2-chlorophenol and 4-nitrophenol were studied using Cu/CeO2 with 4% of copper as catalytic material. The catalyst was prepared by an impregnation method and characterized by X-ray diffraction (XRD), BET surface area, oxygen storage capacity (OSC), temperature programmed reduction (TPR), electron paramagnetic resonance (EPR) and XPS. The reaction was carried out in a batch reactor at T=160 °C and 1.0 MPa. Cu/CeO2 catalyst was found effective in CWAO. On the basis of characterization data, it is suggested that the high activity of the copper–ceria catalyst is related to the modification of the structural and redox properties of the cerium oxide on copper addition. The ratio BOD5/COD was measured to evaluate the biodegradability. Pretreatment by CWAO under operating conditions resulted in effluents whose biodegradation rates were significantly higher than those of the original.

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: 0.10 wt.% Pt/H[Ga]ZSM5, 0.50 wt.% Pt/H[Ga]ZSM5, 1.00 wt.% Pt/H[Ga]ZSM5 and 1.00 wt.% 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 1.00 wt.% Pt/H[Al]MFI catalyst shows an initial global activity four times higher than the 1.00 wt.% 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.

Vanadium nitride and carbide were synthesized by the temperature-programmed reaction of ammonium vanadate (NH 4 VO 3 ) with pure NH 3 and 20% CH 4 in H 2 , respectively. Based on the XRD results, the catalysts showed VN and V 8 C 7 /V 4 C 3 with an amount of V 2 O 3 in the bulk after nitridation and carburization. The hydrogenation, hydrodesulfurization and hydrodenitrogenation reactions were studied and compared to vanadium sulfide catalyst. These catalysts (VC, VN) are stable under typical hydroprocessing conditions.

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 ( X Sn =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 X Sn 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.

One method frequently employed for the preparation of active oxide catalysts consists of partial reduction under hydrogen at elevated temperatures. In this process, it is important to identify well-defined suboxides that can have high catalytic activity and are stable at the elevated temperatures typical of many catalytic reactions. Our results for the reaction of H2 with α-NiMoO4 and β-CoMoO4 show that in situ time-resolved X-ray diffraction is a powerful technique to study the reduction/activation of mixed-metal oxides. It is clearly shown that the mechanism for the reduction of a mixed-metal oxide catalyst can exhibit drastic changes with respect to that observed for simple metal oxide catalysts. The generation of stable suboxides is difficult to predict. Thus, the reaction of H2 with α-NiMoO4 does not lead to formation of a well-ordered NiMoO x intermediate. On the other hand, during the reduction of β-CoMoO4, Co2Mo3O8 and/or CoMoO3 are formed. These chemical transformations are accompanied by changes in the line shape and position of the Mo LII-edge in XANES and affect the behavior of reduced NiMoO4 and CoMoO4 catalysts. Induction times were detected in the reduction process of CoMoO4. From the present results and data previously reported for NiO, it is clear that this phenomenon should be taken into consideration when aiming at the activation of oxide catalysts via reduction in H2.

A hydrocalumite-type material (HC) was synthesized by the co-precipitation method, mixing Ca and Al nitrate solutions in a NaOH solution (pH ≅ 11). This solid was characterized by using different physico-chemical techniques such as: Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), temperature programmed reduction (TPR) and BET surface area measurements. Then, a portion of as-synthesized solid was calcined at 420 ºC (HC 420). Both calcined and pristine solids were impregnated with Mo (15% w/w as MoO3). Ni or Co was also impregnated on Mo/HC or Mo/HC 420 in 1(Co or Ni):3 (Mo) atomic ratios to get catalytic precursors. These solids were also characterized by the above mentioned techniques. Catalytic precursors were tested in the thiophene hydrodesulfuration reaction at 280 ºC and atmospheric pressure. Cobalt promoted catalysts were more active than those promoted with Ni. However, thiophene conversions were lower than that of a conventional CoMo/γ-Al2O3 catalyst.

The combination of two metals in an oxide matrix can produce materials with novel physical and chemical properties. The reactivity of a series of cobalt and nickel molybdates (α-AMoO4, β-AMoO4, and...

Activated-carbon (AC)-supported Ni–Mo sulfide catalysts were prepared employing ammonium thiomolybdate complexes and nickel salts as metal-sulfide precursors and a commercial AC as support. Textural and chemical characterization were carried out by XRD, TPR and BET surface-area measurements. A well-defined Ni(NH 3 ) 6 MoS 4 phase was detected in Ni–Mo/AC co-impregnated samples before pretreatments or catalytic reaction, but it disappeared or became too amorphous to be detected by XRD after prereduction or presulfiding. No relationship between the presence of the mixed phase in the precursor and the HDS activity was obvious. Although both types of pretreatments activated the samples for the hydrodesulfurization (HDS) of thiophene, presulfiding always produced higher activities than prereduction. The nickel salt used (chloride or acetate) did not affect the activity, but the type of thiomolybdate employed had a considerable influence on the HDS activity: The dimeric complex (NH 4 ) 2 Mo 2 S 12 ·2H 2 O was a better precursor than the monomer (NH 4 ) 2 MoS 4 , while the trimer (NH 4 ) 2 Mo 3 S 13 ·1.8H 2 O was the poorer. This is probably related to the different decomposition pathways that follow the complexes, as both, the monomer and dimer, decompose to MoS 2 through amorphous MoS 3 while the trimer directly produces MoS 2 , presumably more crystalline. The monomeric thiotungstate complex (NH 4 ) 2 WS 4 produced a more active Ni–W/AC catalyst than any of the Ni–Mo/AC samples measured, although for the unpromoted samples the situation was the reverse. Comparison with the alumina-supported catalyst suggests that the thiomolybdate derived samples should be further explored for HDS.

Cobalt molybdate and cobalt molybdate-potassium catalysts were found to exhibit activity for alcohol formation from CO2/H2 at 3.0 MPa and 250°C and 300°C. Tetrahedrally coordinated Mo6+ ions favor the selectivity to alcohols. Addition of K2CO3 greatly enhances the selectivity of the reaction to methanol. The extent of this effect was dependent on the way the alkali metal was mixed with the catalyst. Catalysts obtained by mechanical mixing of α-CoMoO4 and K2CO3 deactivate faster than the β-CoMoO4/K mixture calcined at 550°C, where formation of a K2MoO4 phase was detected by XRD. Both catalysts show a similar maximum in selectivity to alcohols at around 90 min of reaction. Addition of potassium by coprecipitation along with Co and Mo, which leads to the formation of K2Co2(MoO4)3, also enhances alcohol production, but the effect is more attenuated than for the other promoted samples.

This study aims at characterizing the properties of pure and sulfided NiMoO4 catalysts using synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) and temperature-programmed reduction (TPR). Mo LII-edge and MIII-edge NEXAFS spectra indicate that on reaction with H2S, the Mo component of NiMoO4 gets partially reduced with the formation of MoS2 type species. For the β-phase of NiMoO4, the sulfidation of Mo is more extensive than for the α-phase, making the former a better precursor for catalysts of hydrodesulfurization (HDS) reactions. The Ni LII-edge features are relatively insensitive to the changes accompanying the partial sulfidation of NiMoO4. The sulfidation of the Ni component is confirmed by analysis of the Ni K-edge extended X-ray absorption fine structure (EXAFS) spectra which show the formation of Ni–S bonds (bond length ∼2.48 A) and a NiMoSx phase. The S K-edge NEXAFS spectra show the presence of at least two types of sulfur species, one associated with a formal oxidation state of 2- and another associated with a formal oxidation state of 6+. We attribute the former to the presence of metal–sulfur bonds (MoSx and NiSy). The latter is associated with the formation of S–O bonds (SO 4 2- ). The formation of sulfates is also supported by the O K-edge NEXAFS spectra. The partially sulfided NiMoO4 catalysts (both α- and β-isomorphs) have a much lower thermal stability in a reducing environment than pure NiMoO4 and MoS2. The sulfided molybdates react with H2 in TPR producing H2O and H2S at temperatures above 400 K.

Well defined Mo2+ surface sites of silica-supported catalyst, produced by H2 reduction of the fixed molybdenum tetraallyl precursor, show a characteristic IR signal at 2170 cm-1 due to adsorbed carbon monoxide. Higher oxidation states of Mo in the same catalyst do not show any signal related to this probe molecule.

The catalytic HDS activities of unsupported sulfided molybdates of Fe(II), Co(II), and Ni(II) have been examined measuring the conversion of thiophene at 400°C under atmospheric pressure. The oxidic precursors employed included the hydratesAMoO4·H2O and the α- and β-AMoO4polymorphs (A=Fe, Co, or Ni). The previous finding that sulfided β-NiMoO4is a better HDS catalyst than α-NiMoO4is now generalized to the other two molybdate systems, suggesting that the tetrahedral environment of Mo in the β-isomorphs provides a more activeA–Mo–S phase than the octahedral one in the α-molybdates. The reduced (nonpresulfided) molybdate samples showed lower HDS activities than those sulfided in pure H2S. Prereduction followed by sulfiding seems to be an optimum procedure for the highest HDS activity of the nickel molybdates and also of β-FeMoO4. It was found that NiMoO4·H2O renders a more active sulfided catalyst than the β-phase synthesized by calcination at 760°C, and this seems to be related to thein situgeneration of β-NiMoO4with higher surface area during the activation of the hydrate at 400°C. The hydrated phase of cobalt behaved similarly, but that of iron, on the contrary, was a poorer catalytic precursor than β-FeMoO4. It is suggested that decomposition of the hydrated compound in the case of Fe could generate a more crystalline material upon sulfiding due to the possibility of changes in the oxidation state of the metals (i.e., Fe2+ ⇄ Fe3+, Mo6+ ⇄ Mo5+) during thermal transformations in presence of evolved water.

Thermal decomposition and hydrogen reduction of ammonium thiomolybdates of formulas: (NH 4 ) 2 [MoS 4 ] (I), (NH 4 ) 2 [Mo 2 (S 2 ) 6 ] · 2H 2 O (II) and (NH 4 ) 2 [Mo 3 S(S 2 ) 6 ] · 1.85H 2 O (III), were investigated using thermogravimetric analysis (TGA), either in pure N 2 or in 10% H 2 in N 2 , and temperature-programmed reduction (TPR). The thiomolybdate compounds were characterized by several physicochemical techniques, including FTIR, PAS/FTIR, UV-visible spectroscopy, XRD and CHNS elemental analyses. The decompositions of (I) and (II) proceed in a similar way independently of the type of gas phase, with production of MoS 3 . However, the anion cluster of (III) is decomposed at lower temperatures in the presence of H 2 . The amorphous MoS 3 compound is very sensitive to the presence of H 2 , which also lowers the onset of its decomposition. These results seem to support a model for the structure of MoS 3 consisting of triangular Mo 3 cluster units, similar to those present in (III). TPR could be used as a “fingerprint” technique for identification of the complexes, as they present strong differences in the shapes and characteristic temperatures of the reductograms.

In this work carbon aerogels were synthesized by catalytic chemical vapor deposition method (CCVD). Ferrocene were employed as a source both of catalytic material (Fe) and of carbon. Gaseous hydrogen and argon were used as reductant and carrier gas, respectively. The products of reaction were collected over alumina. The morphology and textural properties of the soot produced in the reaction chamber were investigated using Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, X-ray photoelectron spectroscopy, and N2physisorption (BET and BHJ methods). After the evaluation of the porous structure of the synthesized products, 780 ± 20 m2/g ofSBETand 0.55 ± 0.02 cm3/g ofVBJHwere found. The presence of iron carbide and the partial oxidation of carbon nanostructures were revealed by XPS.

Sulfided αand β-NiMoO4 have been employed as model HDS catalysts, aiming to investigate the effect of phase composition of the precursor mixed oxide on the physicochemical characteristics and activity of the sulfides. Both sulfides are highly amorphous or microcrystalline, and could not be differentiated by means of XRD. The differences in BET area were also found to be minimal. However, it was found by means of TPR that the stable α-isomorph is reduced at lower temperatures than the unstable β-phase in both the oxidic and sulfided states. Sulfided β-NiMoO4 was found to be a better catalyst for the HDS of thiophene than the sulfided α-isomorph. This could be related to the higher stability of the former in H2, as decomposition of the active, amorphous Ni-Mo-S structures results in less active and more crystalline phases, as found by XRD.

Temperature-programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/γ-Al2O3 catalysts (0-5 wt% NiO; 12 wt% MoO3) calcined at temperatures (TC) between 400 and 800°C. Catalysts were further characterized by XRD, BET area, and ammonia adsorption measurements. Ni/Al2O3 samples showed two broad TPR bands: NiI, at lower temperature (Tm), assigned to a surface phase with similar stoichiometry to NiAl2O4, and the high Tm NiII, assigned to bulk-like NiAl2O4. On increasing TC, NiII area increases at the expense of NiI. Mo/Al2O3 catalysts showed spectra with two peaks which were almost insensitive to varying TC up to 660°C. The low Tm MoI peak was assigned to (partial) reduction of polymolybdates, and the high-Tm MoII to further reduction of polymolybdates plus that of more refractory tetrahedrally coordinated and/or monomeric species. In Ni-Mo catalysts, XRD and NH3 adsorption measurements, together with TPR data, indicate surface interaction between Ni and Mo, probably through the formation of Ni-Mo-O surface phases precursors of β-NiMoO4. Ni facilitated the reduction of Mo, as the Tm of the MoI peak decreased on increasing Ni content between 0 and 5 wt% NiO. This effect was less apparent upon increasing TC, indicating that it is related to the presence of Ni in or near the surface. However, quantitative TPR suggested that no appreciable amount of Ni was reduced simultaneously with MoI, and that the extent of MoI reduction was not affected by varying Ni concentration. In a similar way, Mo facilitated reduction of Ni, as reflected in the lower Tm of the NiI band in presence of Mo. Thus synergistic effects between Ni and Mo may be opperative not only in the sulfided state but also in the oxidic precursor of the catalysts. It is speculated that Ni ions responsible for NiI might be involved in the generation of active Ni-Mo-S phases.

A series of NiCoMo hydrodesulfurization (HDS) catalysts supported on silica was prepared varying the ratio r = Co /( Co + Ni ) between 0 and 1, maintaining Mo and (Co + Ni) concentrations constant. Calcination temperatures employed were 500 and 600°C. The promoter (Co and/or Ni) was present in the precursor as a hydrated molybdate phase that suppressed both anhydrous MoO 3 crystallite growth and decrease in surface area resulting from sintering of the support. Both phenomena occurred in the nonpromoted catalyst after calcining at 600°C, probably by a dehydroxylation process resulting from dislinking of polymolybdates from the silica support. A correlation between TPR and dispersion given by XRD was established, confirming that the dispersion of molybdenum on silica was lower than that on the aluminas previously studied. According to the proposed correlation, sulfidation caused an increase in dispersion in all the catalysts. The presence of anhydrous MoO 3 was held responsible for the formation of amorphous MoO 2 observed by TPR after sulfidation. The increase in dispersion after sulfidation was accompanied by a remarkable increase in the initial HDS activity of both nonpromoted and promoted catalysts. However, the nonpromoted sample showed a pronounced initial deactivation during use. Compared with another similar, but supported on alumina, series of catalysts, a minimum instead of a maximum steadystate HDS activity was found for an intermediate value of r .

The effect of prereduction on CO oxidation activity of unsupported copper-chromite oxide catalysts was examined. Results were found to be in good agreement with two mechanisms for a surface copper enrichment due to CO prereduction which produced an activity increase in the copper-chromite catalyst.

International audience; The photocatalytic degradation of phenol was performed at room temperature in aqueous suspended mixtures of TiO2 and activated carbon (AC). The main objective of the present work was to verify the potential of TiO2/AC system in the photocatalytic degradation of phenol and the principal intermediate products after performing three consecutive runs. The phenol disappearance follows a first-order kinetics. Therefore, the apparent first-order rate constant of phenol and total organic carbon photodegradations were selected to evaluate the photoefficiency of the system. From the present results it can be concluded that there is a synergistic effect between both solids which is determined by the numbers of photocatalytic runs. From a practical point of view, TiO2/AC is able to photomineralize phenol and total organic carbon for three and two, respectively, consecutive runs more efficiently than TiO2 alone.

The phase transitions in a series of CoMoO4 and NiMoO4 catalysts have been studied using time-resolved x-ray diffraction and calculations based on density functional theory. Important differences are observed in the temperatures and energetics for these transitions. X-ray absorption spectroscopy was used to study the sulfidation of the molybdates with H2S and SO2. For small exposures of H2S and moderate temperatures (50–150°C), one sees the formation of sulfides and sulfates on the oxide catalysts. Exposure to large amounts of H2S at elevated temperatures (350–400°C) leads to formation of pure NiMoSx and CoMoSx compounds (no SOx species) that are active as HDS catalysts. CoMoO4 and NiMoO4 are good sorbents for sulfur dioxide. The adsorption of SO2 on the molybdates at room temperature produces SO3 and SO4 species without dissociation of SO2. Most of the SO3 and SO4 species decompose after heating to 400°C. The sulfided CoMoO4 and NiMoO4 catalysts can be “regenerated” by heating in O2 at 500°C.

The initial hydrodesulfurization activity behavior of supported nickel molybdate catalysts has been found to be markedly influenced by the presence of the promoter (nickel). The promoter diminished both the rate and the extent of deactivation of the fresh catalyst when exposed to a mixture of hydrogen and thiophene at atmospheric pressure. Presulfidation of the catalysts with pure H 2 S did not affect the optimum nickel concentration but increased the optimum molybdenum concentration. These results together with those obtained on surface acidity, carbon deposition, and sulfidation extent seems to support the idea that the positive influence of the promoter on the initial transformation of the catalyst is to maintain the dispersion of molybdenum during the sulfidation of the catalyst and to diminish carbon deposition.