TPR Experiments Research Articles

CeO2 and Co3O4–CeO2 nanoparticles: effect of the synthesis method on the structure and catalytic properties in COPrOx and methanation reactions

CeO2 and Co3O4–CeO2 nanoparticles were synthesized, thoroughly characterized, and evaluated in the COPrOx reaction. The CeO2 nanoparticles were synthesized by the diffusion-controlled precipitation method with ethylene glycol. A notably higher yield was obtained when H2O2 was used in the synthesis procedure. For comparison, two commercial samples of CeO2 nanoparticles (Nyacol®)—one calcined and the other sintered—were also studied. Catalytic results of bare CeO2 calcined at 500 °C showed a strong influence of the method of synthesis. Despite having similar BET area values, the CeO2 synthesized without H2O2 was the most active sample. Co3O4–CeO2 catalysts with three different Co/(Co + Ce) atomic ratios, 0.1, 0.3, and 0.5, were prepared by the wet impregnation of the CeO2 nanoparticles. TEM and STEM observations showed that impregnation produced mixed oxides composed of small CeO2 nanoparticles located both over the surface and inside the Co3O4 crystals. The mixed oxide catalysts prepared with a cobalt atomic ratio of 0.5 showed methane formation, which started at 200 °C due to the reaction between CO2 and H2. However, above 250 °C, the reaction between CO and H2 became important, thus contributing to CO elimination with a small H2 loss. As a result, CO could be totally eliminated in a wide temperature range, from 200 to 400 °C. The methanation reaction was favored by the reduction of the cobalt oxide, as suggested by the TPR experiments. This result is probably originated in Ce–Co interactions, related to the method of synthesis and the surface area of the mixed oxides obtained.

Green propene through the selective hydrogenolysis of glycerol over supported iron-molybdenum catalyst: The original history

The hydrogenolysis of glycerol, a byproduct of biodiesel production, to propene was studied over supported metallic catalysts. About 100% glycerol conversion was observed for all catalysts, but the selectivity was dependent on the composition. Ru and Pd on activated carbon produced mainly propane and methane/ethane, respectively. Ni/Mo on activated carbon gave mainly propane, whereas Zn/Mo and Cu/Mo supported on activated carbon produced intermediate oxygenated compounds. Fe/Mo over activated carbon presented up to 90% selectivity to propene. This results may be explained in terms of the poor reductibility of the Fe/Mo catalysts, as shown by TPR and XRD experiments. A possible pathway from glycerol to propene involves the formation of acetol, 1,2-propanediol and 2-propanol as intermediates.

Reductive pyrolysis of Miocene-aged lignite humic acids, Bulgaria

Atmosphere Pressure–Temperature Programmed Reduction (AP–TPR) technique coupled “off-line” with thermal desorption gas chromatography–mass spectrometry (TD-GC/MS) can be effectively used to specify qualitatively/quantitatively organic functionalities in humic substances. The AP–TPR technique has been initially developed and successfully applied for sulphur speciation in coals and in their biodesulphurized products. The aim of the present study is to analyze volatiles in flue gases of a reductive pyrolysis of Miocene-aged lignite humic acids by AP–TPR “off-line” TD-GC/MS and to assign identified components to the structural compositions of the samples studied.Humic acids from two coal-bearing provinces in Bulgaria, i.e. Thrace and Sofia, have been considered. The following compounds were tracked and quantified in the flue gases released during the AP–TPR experiments: aliphatics, i.e. nC6–nC14, mono unsaturated/saturated pairs, alkylated benzenes, styrenes, naphthalenes, biphenyls, fluorene, acenaphthylene; oxygen containing compounds, i.e. phenols, methoxy phenols, furans, benzofurans; sulphur containing compounds, i.e. sulphides, thiophenes, benzothiophenes; nitrogen containing compounds, i.e. pyrroles, indoles, quinolines, benzonitriles, etc.Total content of organics in pyrolysates amounts to 55.9mg/g Corg for Thrace humic acids (Maritza-East deposit) and 55.0mg/g Corg for Sofia humic acids (Stanjanci deposit). Alkyl benzenes (C6–C10) highly dominate in the programs up to half of the recorded components (46–58rel.%). The low sample maturity is reflected in high abundance of phenols, C6–C8 (20rel.%), methoxy phenols (2.7rel.%) and degradation products from carbohydrates, i.e. furaldehydes, 2-cyclopenten-1-ones, etc. Plots of four group composites, i.e. aliphatics, aromatics, O-, S- and N-containing compounds, in “spider web” diagram seem promising for bulk interpretation of pyrolysates data.According to the reductive pyrolysis data, structural units of Miocene-aged humic acids are composed by 1–2 aromatic rings, condensed or coupled, including heteroatoms arranged in linear and cyclic forms.

Comparison of Cu/BEA, Cu/SSZ-13 and Cu/SAPO-34 for ammonia-SCR reactions

In this study, the ammonia-SCR process was investigated using 2.5wt.% Cu/BEA, 2.6wt.% Cu/SAPO-34 and 3.1wt.% Cu/SSZ-13. Several reactions such as NO oxidation, ammonia oxidation, standard SCR, fast SCR and NO2 SCR were studied to understand the effect of zeolite type. It was found that the small-pore zeolites/silicoaluminophosphates with CHA structure (Cu/SAPO-34 and Cu/SSZ-13) exhibited higher SCR activity at 150°C and lower selectivity toward N2O formation during standard SCR conditions than Cu/BEA. However, formation of ammonium nitrate species during fast SCR conditions at 150°C occurred over Cu/CHA catalysts, which resulted in a gradual decrease of the NOx conversion. Such blocking was also observed over Cu/BEA, albeit to a minor extent. The ammonium nitrate formation and its decomposition temperature regimes resulted in that the Cu/BEA was catalytically more active at lower temperature than either Cu/SAPO-34 or Cu/SSZ-13 during fast SCR conditions. Additionally, our results show that the ammonium nitrate species were more stable on the small-pore zeolites than on Cu/BEA. Comparing the two Cu/CHA catalysts, Cu/SAPO-34 and Cu/SSZ-13, it was found that ammonia oxidation at high temperatures and ammonia SCR at 150°C was higher on Cu/SAPO-34. Further, TPR experiments showed that Cu in Cu/SAPO-34 is more easily reduced compared to Cu/SSZ-13. This can facilitate the redox processes and can thereby be a reason for the higher activity at 150°C for Cu/SAPO-34. In addition, Cu/SAPO-34 forms less N2O and this might be a result of the formation of more stable ammonium nitrates. To conclude, the choice of the type of zeolite/silicoaluminophosphates affects the activity and selectivity of the different steps in the SCR process.

Chemical-loop reforming of ethanol over metal ferrites: An analysis of structural features affecting reactivity

This paper deals with an investigation of the reactivity of spinel type mixed oxides, i.e., magnetite and Ni-ferrite, in the chemical-loop reforming of ethanol to COx and H2. The two compounds showed a similar behavior during the oxide reduction, but the Ni ferrite showed a higher activity in ethanol anaerobic oxidation and decomposition, which was also confirmed by TPR experiments. During the first minutes of reaction, when the materials still acted as reactants while being reduced at the same time, the two oxides showed differences in regard to the nature of the products formed. During reduction, the structural evolution was monitored by means of several physical techniques, thus showing the formation of Fe carbide and metallic species as well. The re-oxidation step, carried out with steam, led to the generation of H2 but also to COx arising from the carbide transformation and the refoming of the carbon residues accumulated during the reduction step. Although the iron carbide was totally oxidized, the carbon residues could not be completely removed during steaming.

Selective Catalytic Reduction of NOx of Ship Diesel Engine Exhaust Gas with C3H6 over Cu/Y Zeolite

Various solid Cu-containing catalysts were prepared. Their performance in the selective catalytic reduction of NOx using propene as reducing agent from 150 to 450 °C in an O2-rich model exhaust gas in the presence of water vapor was investigated. This research aimed at the development of a catalytic NOx to N2 (DeNOx) step to be part of a ship diesel exhaust abatement system in combination with other techniques, such as nonthermal plasma. Among the catalysts tested, Cu on zeolite Y with an optimized load of 16 wt % (denoted as 16Cu/Y) displayed excellent DeNOx activity with highest selectivity toward N2 at 290 °C. The influence of other variables, such as Cu load, calcination temperature, feed composition, and GHSV on the performance of 16Cu/Y was studied, as well. The highest N2 yield of 98% was achieved using 2000 ppm of propene in the gas feed. The presence of O2 proved to be a crucial factor for promoting the selective reduction of NOx with C3H6 over this catalyst. On the other hand, the presence of water in the feed decreased NOx to N2 conversion. However, the catalyst showed excellent stability over 120 h, even at high water concentration, and also after repeated heating from ambient temperature to 450 °C, and it was reusable after downtimes without remarkable loss in activity. The nature of the Cu species was studied by XPS, XRD, and TPR experiments.

Fluidizable Ni/La2O3-γAl2O3 catalyst for steam gasification of a cellulosic biomass surrogate

This study reports a new fluidizable Ni catalyst supported on La2O3 modified γ-Al2O3. The 20% Ni/5% La2O3-γAl2O3 catalyst is prepared using a specially designed multistep incipient wetness technique and direct reduction of metal nitrate precursors. Steam gasification of glucose (a biomass surrogate), is developed in a CREC Riser Simulator using the new fluidizable catalyst. Experiments are performed at different steam/biomass ratios, temperatures and reaction times. Catalytic gasification runs confirm the high performance of the Ni/La2O3-γAl2O3 in terms of reforming activity, and reduced coke formation. Furthermore, observed gasification products (H2, CO, CO2, and CH4) are in agreement with thermodynamics, with product yields approaching chemical equilibrium as the reaction time is increased. Furthermore, the value of the Ni/La2O3-γAl2O3 catalyst is demonstrated while comparing its improved performance with respect to the one of other prepared catalysts: (i) an unpromoted Ni/γAl2O3 and (ii) a Ni/La2O3-γAl2O3 prepared via metal precursor calcination. Prepared catalysts are also characterized using BET surface area analysis, TPR, TPO, H2-pulse chemisorption, pyridine FTIR, CO2 and NH3 TPD. It is shown that the addition of lanthanum oxides reduces surface area losses, increasing the thermal stability of γ-Al2O3. La2O3 also improves reducibility and dispersion of the active phase by decreasing nickel-aluminate formation. Pyridine FTIR confirms the absence of Brønsted acid sites in γ-Al2O3, with La2O3 reducing Lewis acidity. Multiple TPO and TPR experiments also show that the prepared catalyst remains stable under repeated oxidation and reduction cycles. As a result, it is proven that the enhanced gasification activity of the Ni/La2O3-γAl2O3 fluidizable catalyst of the present study is in line with their various and favorable structural properties (available Ni surface area and basicity/acidity ratio) modifications.

Ni-substituted LaMnO3 perovskites for ethanol oxidation

The B-site substitution of LaMnO3 perovskites by Ni was investigated under the oxidation of ethanol. Proper characterization techniques, including BET surface area measurement, XRD, FTIR, XPS, TPR, O2-TPD, and FE-SEM experiments were performed to survey the physicochemical properties of perovskites. The results reveal that up to 25% of Mn can be replaced by Ni; beyond this limit, segregated NiOx can be synthesized. Inserting Ni into the solid solution of perovskite yields unique bridging lattice oxygen sites (Ni–O–Mn) in Ni-doped LaMnO3. Based on catalytic performance in ethanol oxidation, the Ni–O–Mn sites are likely to promote ethanol conversion and the oxidation of acetaldehyde to CO2 at low reaction temperatures. The abatement of intermediates over Ni–O–Mn sites is hypothesized and a plausible reaction pathway is proposed. Moreover, the time on-stream testing revealed that the interaction between Ni and Mn is likely to enhance perovskite's thermal stability in ethanol oxidation.

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al2O3 catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H2-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al2O3 supports and the promotion of NiO reduction by Pr modification. The CH4 conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al2O3 catalysts maintained the high activity after 48 h while Ni/Al2O3 had a significant deactivation.

Effect of Sn surface states on the photocatalytic activity of anatase TiO2

The influence of surface Sn-doping on the photocatalytic properties of anatase TiO2 has been investigated in samples prepared by a grafting route using Sn(IV) tert-butoxide as Sn precursor. The grafting procedure leads to the formation of isolated Sn(IV) sites on the surface of anatase TiO2 powders as gauged by structural characterisation based on XRD, Raman spectroscopy and XAS. Studies of the surface reduction based on TPR experiments and XPS provide the conditions for a selective reduction of surface Sn(IV) to the divalent oxidation state. Electronic structure characterisation based on valence band XPS and DRS shows that there is a slight widening of the band gap upon Sn(IV)-grafting, but Sn(II) related states emerge at the top of the main valence band upon reduction at temperatures up to 350°C, and this induces visible light absorption. Grafting of TiO2 with Sn(IV) increases the formation rate of OH radicals on the surface of the material. Reduction of the Sn(IV)-grafted TiO2 to form surface Sn(II) brings about substantial increase of the photocatalytic efficiency for the methylene blue degradation under irradiation with λ≥320nm compared with Sn(IV)-grafted and pure anatase TiO2. This observation is explained based on a surface hole trapping by the Sn(II)-related surface states which lie above the top of the main valence band and can therefore act as trapping sites for holes produced under photoexcitation.

Spectroscopic characterization of Mn–Co–Ce mixed oxides, active catalysts for COPROX reaction

Mn–Co–Ce mixed oxides are active and selective catalysts for the CO preferential oxidation (COPROX), which is a promising process for the purification of hydrogen streams. In this work, we report a careful spectroscopic characterization of the said system, with the aim of relating its physical chemistry properties to the catalytic behavior. In all the Co–Mn–Ce samples, we detected the formation of partially developed (Mn,Co)3O4 mixed spinels. The presence of these species, which can be reduced during the TPR experiments at an intermediate temperature range (300–600 °C), was also suggested by XRD and LRS. XPS results show that in all cases the catalytic surface is enriched in Mn, while the opposite occurs for Co. As regards the catalytic activity, we observed that the best formulations were those containing intermediate Mn/Co ratios (1/4 and 1/1), which can be ascribed to the promoting effect of Mn in improving the redox properties of Co active sites and provoking an increase in surface area. The best catalyst, which has a Mn/Co ratio of 1/4, was very stable after 75 h of time-on-stream with CO2 included in the feed.

Synergetic effects of mixed copper–iron oxides oxygen carriers in chemical looping combustion

Chemical looping combustion (CLC) is an emerging technology for clean energy production from fuels. CLC produces sequestration-ready CO2-streams without a significant energy penalty. Development of efficient oxygen carriers is essential to successfully operate a CLC system. Copper and iron oxides are promising candidates for CLC. Copper oxide possesses high reactivity but it has issues with particle agglomeration due to its low melting point. Even though iron oxide is an inexpensive oxygen carrier it has a slower reactivity. In this study, mixed metal oxide carriers containing iron and copper oxides were evaluated for coal and methane CLC. The components of CuO and Fe2O3 were optimized to obtain good reactivity while maintaining physical and chemical stability during cyclic reactions for methane-CLC and solid-fuel CLC. Compared with single metal oxygen carriers, the optimized Cu–Fe mixed oxide oxygen carriers demonstrated high reaction rate, better combustion conversion, greater oxygen usage and improved physical stability.Thermodynamic calculations, XRD, TGA, flow reactor studies and TPR experiments suggested that there is a strong interaction between CuO and Fe2O3 contributing to a synergistic effect during CLC reactions. The amount of oxygen release of the mixed oxide carrier in the absence of a fuel was similar to that of the single metal oxides. However, in the presence of fuels, the oxygen consumption and the reaction profiles of the mixed oxide carriers were significantly better than that of the single metal oxides. The nature of the fuel not only influenced the reactivity, but also the final reduction status of the oxygen carriers during chemical looping combustion. Cu oxide of the mixed oxide was fully reduced metallic copper with both coal and methane. Fe oxide of the mixed oxide was fully reduced Fe metal with methane but it was reduced to only FeO with coal. Possible mechanisms of how the presence of CuO enhances the reduction of Fe2O3 are discussed.

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

A series of model catalysts were prepared by depositing different size Pd(n) clusters on alumina films grown to variable thickness on a Ta(110) support. Samples were characterized by a combination of X-ray photoelectron spectroscopy, low energy He+ scattering, and temperature-programmed reaction and desorption (TPR/ TPD). For the activity studies, the samples were first exposed to 18O2 at Tox, and then to 13CO at 180 K, where CO sticks to Pd, but not to the alumina support. CO oxidation activity increased with increasing thickness of the alumina support up to approximately 4.5 nm, but was constant for greater thicknesses. Activity increased, with Tox up to 400 K, but then declined for Tox = 500 K. Activity was also found to be non-monotonically dependent on deposited cluster size, with Pd(n) (n < or = 6) being generally more reactive than the larger clusters studied. Activity was only weakly correlated with exposed Pd binding sites, which decreased with increasing cluster size, however, there does appear to be a correlation between activity and electronic structure, as probed via the Pd 3d binding energy. Unlike previous systems we have studied, the activity of small Pd(n) on these alumina films was quite stable, with essentially no changes observed in up to eight successive TPR experiments.

Citric acid loading for MoS2-based catalysts supported on SBA-15. New catalytic materials with high hydrogenolysis ability in hydrodesulfurization

The aim of this work is to get a deeper insight into the effect of citric acid (CA) loading in NiMo sulfided catalysts supported on SBA-15 on their behavior in hydrodesulfurization (HDS). Catalysts were prepared by simultaneous impregnation of Ni, Mo and CA species, varying the CA amount in aqueous solution. After the impregnation, NiMoCA catalysts were dried at 100°C under air atmosphere without calcination. Catalysts were characterized by several techniques (TGA, N2 physisorption, small-angle and powder XRD, FT-IR, UV–vis DRS, TPR, elemental analysis and HRTEM) and tested in HDS of dibenzothiophene (DBT). N2 physisorption, small-angle XRD and FT-IR showed the adsorption of CA on the SBA-15 surface. XRD characterization demonstrated that Ni and Mo oxide species were well dispersed in all catalysts. UV–vis DRS revealed better dispersion of Mo species with the increase of CA loading. TPR experiments exhibited an important effect of CA under reducing atmosphere; it can be reduced to leave carbon on the catalytic materials. This observation was confirmed by carbon analysis which showed an increase in the amount of carbon in the same direction than the CA loading. HDS of DBT showed differences in activity and selectivity of the catalysts prepared with different CA loading. We observed outstanding promotion of direct desulfurization (DDS) route with increasing the CA amount. The preference of DBT to react over NiMoCA catalysts toward DDS route was an unexpected behavior.

Deep desulfurization of gas oil over NiMo catalysts supported on alumina–zirconia composites

A series of NiMo catalysts supported on Al2O3–ZrO2 composites containing 0, 2.5, 5 and 10wt.% ZrO2 was synthesized, characterized and evaluated for deep desulfurization of gas oil. X-ray diffraction patterns of the supports indicate homogenous dispersion of 2.5–10wt.% of ZrO2 in bulk Al2O3. Mono-modal pore-size distribution was observed with a decrease in average pore-size with increasing ZrO2 content. NH3-TPD results show that incorporation of 5wt.% or more ZrO2 neutralized the weak acid sites of Al2O3 and generated a different type of stronger acid sites. UV–Visible diffuse reflectance spectroscopy results indicate the presence of tetrahedral and octahedral Mo6+ ions species along with an increase in octahedral species with addition of ZrO2 possibly due to weaker interaction of active metals and composite support. This result is also supported by H2-TPR and CO chemisorption measurements. Deep desulfurization of gas oil, carried out in a bench-scale flow reactor at 320, 340 and 360°C, indicate that the addition of ZrO2 increased the catalytic activity – especially at higher temperature. Compared to Al2O3-based catalyst, the 1.5 order HDS rate constant was about 1.3, 1.8 and 2.5 times higher for catalysts containing 2.5, 5 and 10wt.% ZrO2, respectively. A correlation was found between the enhancement of hydrogenation activity of sulfided catalysts and the reducibility of their oxide precursors, as determined by the amount of hydrogen consumed in TPR experiments followed by mass spectroscopy.

A study on the effect of support's reducibility on the reverse water-gas shift reaction over Pt catalysts

In this study, the effect of the reducibility of the support on the mechanism of the reverse water gas shift reaction over Pt/TiO2 and Pt/Al2O3 catalysts was examined using a differential and fixed bed reactor. The kinetic study showed that the reverse water gas shift reaction using the Pt/TiO2 and Pt/Al2O3 catalysts were consistent with the redox mechanism. An elementary reaction test and XPS analysis further confirmed that the reverse water gas shift reaction proceeded through the redox mechanism via oxidation and reduction at the Pt sites and reducible support sites on the catalyst surface. In the H2 TPR and FT-IR experiments, the Pt/TiO2 was shown to have a new active site located at the metal–support interface. Therefore, the Pt/TiO2 catalyst produced greater CO2 conversion and TOFs due to the presence of the new active site, which resulted from the strong metal–support interaction and higher reducibility of the support relative to the Pt/Al2O3 catalyst.

Fischer-Tropsch Synthesis Over Co/Al2O3Catalyst-Effect of Pretreatment Procedures

Abstract Due to high activity of cobalt metal in syngas conversion to higher hydrocarbons and long chain normal paraffins, supported cobalt catalysts have been widely used for Fischer-Tropsch synthesis (FTS) reaction. We investigated effect of pretreatment procedures on catalytic performance of 15wt% Co/Al2O3 catalyst prepared by incipient wetness impregnation (IWI). Catalyst was characterized by different methods such as BET, XRD, TPR, TGA, H2-TPD and TPH/TPO-MS. FTS was performed in a fixed-bed reactor at the following conditions: 593 K, 20 bar, H2/CO = 2 and gas space velocities of 3.85 NL/g-cat/h. The catalyst was activated in situ with either hydrogen at 648 K for 12 h, or syngas (CO/H2/He) or 10%CO/Ar at 623 K for 12 h. BET surface areas of calcined catalyst was 154 m2/g. XRD pattern of calcined catalyst showed existence of cubic Co3O4 in addition to -Al2O3 phase. Metallic cobalt (Co fcc) was found after H2 reduction. Co°(fcc and hcp) and CoxC (x = 2, 3) were found in samples activated in syngas and 10%CO/Ar. Two step reduction of Co3O4 was observed in TPR and TGA experiments. Carbon deposition was observed during TGA using 10%CO/Ar as reducing agent. Degree of reduction was about 83% (H2-TPR following H2 isothermal activation) and dispersion 9.8%. Corrected value of crystallite sizes from combination of chemisorption and H2-TPR following hydrogen isothermal activation was 9.8 nm. TPH/TPO-MS results indicate existence of CoxC and different types of deposited carbon including graphitic carbon after syngas-activation. CO conversion of 10%CO-activated catalyst was very low (7.4%) whereas the H2-activated catalyst was the most active (CO conversion of 58.8%). CH4 selectivity decreased and C+ selectivity increased, with increasing amount of H2 in the reducing gas. Moreover, the hydrogen reduced catalyst had the highest 1-olefin selectivity (C3-H5 hydrocarbons). These results show that surface carbide sites (created after 10%CO/Ar and syngas pretreatments) favor methane production and secondary hydrogenation of 1-olefins. In conclusion, H2-activated 15wt% Co/Al2O3 catalyst had the best performance due to high degree of reduction and dispersion.

Nickel and nickel–platinum as active and selective catalyst for the maleic anhydride hydrogenation to succinic anhydride

Pt, Ni, Co, Cu and bimetallic Pt–Ni, Pt–Co, Pt–Cu catalysts supported on γ-Al 2O 3 have been studied for the hydrogenation maleic anhydride (MA) to succinic anhydride (SA). X-ray diffraction (XRD) and H 2 temperature programmed reduction TPR studies were performed to characterize the catalysts. The flow reactor studies demonstrated that Pt–Ni bimetallic catalyst is highly active and selective for the hydrogenation of MA. Hydrogenation of maleic anhydride produced mainly succinic anhydride and γ-butyrolactone, and the selectivity toward γ-butyrolactone increased with pressure. Using Al 2O 3 as support, it was possible to obtain the highest reaction rate ever obtained with 90% selectivity to SA at 100% conversion. The process appears to be controlled by H 2 dissociation on nickel and the catalytic activity can be further improved, without loss of selectivity, by adding a very small amount of Pt(0.3) to increase the rate of H 2 dissociation. TPR experiments show high-temperature reduction peaks in monometallic Ni catalysts. When Pt is present, the formation of Pt–Ni compound provokes the shift of the reduction peaks and the appearance of new reduction signals.

Co–Pd/γ‐Al2O3 catalyst for heavy oil upgrading: Desorption kinetics, reducibility and catalytic activity

AbstractThe influence of Pd on a Co–Pd/γ‐Al2O3 heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH3 desorption is found to be less for Co–Pd/γ‐Al2O3 sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H2‐pulse chemisorptions study. When evaluated using VGO as feed stock, the Co–Pd/γ‐Al2O3 displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ‐Al2O3 catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst.

Rh–Ni/CeO2–Al2O3 catalysts for methane dry reforming

A series of Ni and Rh–Ni catalysts supported on Al2O3 modified by CeO2 (3 and 5wt%, Ce) was studied for CO2 reforming of methane. Catalysts were characterized by hydrogen chemisorption, TPR, XRD, XPS, BET, TEM and dry reforming reaction tests. The influence of calcination temperature and Ce loading on activity and stability of mono and bimetallic samples was studied. The effect of Rh and Ce addition to Ni/a-Al2O3 catalyst improves the activity. Results show that the catalyst content 3%w/w Ce calcined at 650°C, present higher reforming activity and stability than the unpromoted catalyst. The higher catalytic activity is attributed to the interaction between Rh and Ce phases, which has been verified by TPR experiments that improve the Rh dispersion and increase the catalyst active surface. The Rh addition on Ce–Al2O3 support increases the resistance to deactivation by carbon deposition.