Catalytic Hydroprocessing of p-Cresol: Metal, Solvent and Mass-Transfer Effects

A systematic study of the comparative performances of supported Pt, Pd, Ru and conventional CoMo/Al₂O₃, NiMo/Al₂O₃, NiW/Al₂O₃ catalysts as well as the effects of solvent, H₂ pressure and temperature on the hydroprocessing activity of a representative model bio-oil compound (e.g., p-cresol) is presented. With water as solvent, Pt/C catalyst shows the highest activity and selectivity towards hydrocarbons (toluene and methylcyclohexane), followed by Pt/Al₂O₃, Pd and Ru catalysts. Calculations indicate that the reactions in aqueous phase are hindered by mass-transfer limitations at the investigated conditions. In contrast, with supercritical n-heptane as solvent at identical pressure and temperature, the reactant and H₂ are completely miscible and calculations indicate that mass-transfer limitations are eliminated. All the noble metal catalysts (Pt, Pd and Ru) show nearly total conversion but low selectivity to toluene in supercritical n-heptane. Further, conventional CoMo/Al₂O₃, NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts do not show any hydrodeoxygenation activity in water, but in supercritical n-heptane, CoMo/Al₂O₃ shows the highest activity among the tested conventional catalysts with 97?% selectivity to toluene. Systematic parametric investigations with Pt/C and Pt/Al₂O₃ catalysts indicate that with water as the solvent, the reaction occurs in a liquid phase with low H₂ availability (i.e., low H₂ surface coverage) and toluene formation is favored. In supercritical n-heptane with high H₂ availability (i.e., high H₂ surface coverage), the ring hydrogenation pathway is favored leading to the high selectivity to 4-methylcyclohexanol. In addition to differences in H₂ surface coverage, the starkly different selectivities between the two solvents may also be due to the influence of solvent polarity on p-cresol adsorption characteristics.     

Production of middle distillate through hydrocracking of paraffin wax over Pd/SiO2–Al2O3 catalysts

Pd/SiO₂–Al₂O₃ catalysts (Pd/SA-X) with different SiO₂ contents (X, wt%) were prepared for use in the production of middle distillate (C₁₀–C₂₀) through hydrocracking of paraffin wax. The effect of SiO₂ content of Pd/SA-X catalysts on their physicochemical properties and catalytic performance in the hydrocracking of paraffin wax was investigated. High surface area and well-developed mesopores of Pd/SA-X catalysts improved the dispersion of Pd species on the SiO₂–Al₂O₃ support. Acidity of Pd/SA-X catalysts determined by NH₃-TPD experiments showed a volcano-shaped trend with respect to SiO₂ content. Conversion of paraffin wax increased with increasing acidity of the catalyst, while selectivity for middle distillate decreased with increasing acidity of the catalyst. Yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that acidity of Pd/SA-X catalysts played an important role in determining the catalytic performance in the hydrocraking of paraffin wax. Among the catalyst tested, Pd/SA-69 with moderate acidity showed the highest yield for middle distillate.     

Effect of Phosphorus Precursor,Reduction Temperature,and Support on the Catalytic Properties of Nickel Phosphide Catalysts in Continuous-Flow Reductive Amination of Ethyl Levulinate

Levulinic acid and its esters (e.g., ethyl levulinate, EL) are platform chemicals derived from biomass feedstocks that can be converted to a variety of valuable compounds. Reductive amination of levulinates with primary amines and H₂ over heterogeneous catalysts is an attractive method for the synthesis of N-alkyl-5-methyl-2-pyrrolidones, which are an environmentally friendly alternative to the common solvent N-methyl-2-pyrrolidone (NMP). In the present work, the catalytic properties of the different nickel phosphide catalysts supported on SiO₂ and Al₂O₃ were studied in a reductive amination of EL with n-hexylamine to N-hexyl-5-methyl-2-pyrrolidone (HMP) in a flow reactor. The influence of the phosphorus precursor, reduction temperature, reactant ratio, and addition of acidic diluters on the catalyst performance was investigated. The Ni₂P/SiO₂ catalyst prepared using (NH₄)₂HPO₄ and reduced at 600 °C provides the highest HMP yield, which reaches 98%. Although the presence of acid sites and a sufficient hydrogenating ability are important factors determining the pyrrolidone yield, the selectivity also depends on the specific features of EL adsorption on active catalytic sites.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

Dehydrogenation of isobutane over Sn/Pt/Na-ZSM-5 catalysts: The effect of SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratio,amount and distribution of Pt nanoparticles on the catalytic behavior

Sn/Pt/Na-ZSM-5 was used as catalyst for the dehydrogenation of isobutane, and the effect of SiO₂/Al₂O₃ ratio and the dispersion of Pt nanoparticles on the conversion and product selectivity were studied under atmospheric pressure at 848 K. The catalysts were characterized by various techniques such as H₂ chemisorption, TEM, SEM, EDX, XRD, FT-IR, TG/DTG, elemental analysis by XRF and ICP techniques. Higher dispersion of Pt nanoparticles in the catalyst with SiO₂/Al₂O₃ ratio of 40 resulted in higher selectivity for isobutene.     

Preparation of alkali-resistant, Sil-1 encapsulated nickel catalysts for direct internal reforming-molten carbonate fuel cell

A thin layer of silicalite-1 zeolite membrane was grown on the surface of Ni/SiO₂ and Ni/Al₂O₃ catalyst beads after seeding and secondary regrowth to create core–shell catalysts that are resistant to alkali poisoning from direct internal reforming-molten carbonate fuel cell (DIR-MCFC). The zeolite shell thickness was optimized to prevent poisoning and minimize diffusion resistance. An out-of-cell test was designed to simulate the fuel cell operating conditions, which showed that the new core–shell catalysts maintained a high activity similar to the original fresh catalyst in spite of the exposure to alkali vapor at high temperature. The conventional Ni/SiO₂ and Ni/Al₂O₃ catalysts suffered higher than 80% decrease in activity for steam reforming of methane reaction (SRM).     

Acetylation of phenol with Al-MCM-41

Mesoporous Al-MCM-41 molecular sieve materials with three different SiO₂/Al₂O₃ ratios were used as catalysts for the acetylation of phenol with acetic anhydride and acetic acid as the acetylating agents. The reactions gave 100% ortho-selectivity with acetic acid being the more effective acylating agent. The reactions were run under different conditions of temperature, feed flow rate, reactant mole ratio and SiO₂/Al₂O₃ ratio of the catalyst and all the variables were shown to have significant influence on the acetylation of phenol. A possible reaction mechanism is also suggested.     

Effect of Al2O3/SiO2 ratio on iron-based catalysts for Fischer–Tropsch synthesis

A systematic study was undertaken to investigate the effects of Al₂O₃/SiO₂ ratio on reduction, carburization and catalytic behavior of iron-based Fischer–Tropsch synthesis (FTS) catalysts promoted with potassium and copper. The catalysts were characterized by N₂ physical adsorption, CO₂ temperature-programmed desorption (TPD), H₂ temperature-programmed reduction (TPR) and Mössbauer effect spectroscopy (MES). CO₂-TPD indicated that Al₂O₃ binder has stronger acidity than SiO₂ binder and weakens the surface basicity of the catalysts. H₂-TPR profiles suggested that the lower Al₂O₃/SiO₂ ratio promotes the reduction of Fe₂O₃→Fe₃O₄. With further increasing Al₂O₃/SiO₂ ratio, the transformation of Fe₂O₃→Fe₃O₄ shifts to higher temperatures. The MES results showed that the increase of Al₂O₃/SiO₂ ratio leads to the relatively large crystallite size of α-Fe₂O₃ and inhibits carburization of the catalyst. During reaction tests in a fixed bed reactor it was found that a maximum in catalyst activity is noted at the Al₂O₃/SiO₂ ratio of 5/20 (weight basis). The selectivity to olefins shows a rapid decrease and the formations of methane and light hydrocarbons are promoted with increasing Al₂O₃/SiO₂ ratio. The oxygenate selectivity in total products increases with increasing Al₂O₃/SiO₂ ratio.     

Role of tungsten in supported Pt-W reforming catalysts Part II. Influence of the tungsten loading and metal-support interactions effect

Support Pt-W catalysts are studied for 3-methylhexane reforming. The increase in tungsten loading and the use of SiO₂ support instead of Al₂O₃ in Pt-W catalysts leads to the decrease in total activity and aromatization selectivity. X-ray Photoelectron Spectroscopy (XPS) has been applied to bimetallic Pt-W/Al₂O₃ and SiO₂ catalysts with different Pt/W ratios to try to explain the catalytic results. Observations lead to the conclusion that tungsten species are strongly anchored on the support in Pt-W/Al₂O₃ catalysts at low tungsten concentration. In this case, tungsten species are not reducible (oxidation state +VI) and not accessible catalytically; tungsten is hindered by small Pt particles. At large tungsten loadings, beyond the theoretical monolayer capacity of the support, a fraction of tungsten species migrates to the surface and becomes reducible. This fraction of tungsten-reducible species and large platinum particles are accessible on the surface, but another fraction of tungsten species strongly anchored on the support remains not accessible and not reducible. A model is proposed.     

Gas-Phase Hydroformylation of Propene over Silica-Supported PPh3-Modified Rhodium Catalysts

Heterogeneous rhodium catalysts supported on SiO₂ were modified with PPh₃ for the gas-phase hydroformylation of propene to produce n- and isobutanal. High selectivity to aldehydes was achieved, with no propane or alcohols formed. Investigation of the effects of reaction temperature, reactant partial pressures, total pressure, and PPh₃/Rh ratio suggested that the supported catalyst behaved similarly to the homogeneous catalyst. In particular, the supported catalyst showed similar activation energies and partial and total pressure dependences of the reaction rates to those observed in homogeneous, liquid-phase reactions. The first order dependence of the hydroformylation rate on the partial pressures of propene, CO, and H₂ individually led to a cubic dependence of butanal formation on total pressure for equimolar reactant mixtures. High regioselectivity with a typical n/i ratio of 14 was achieved.     

Large enhancement in methane-to-syngas conversion activity of supported Ni catalysts due to precoating of catalyst supports with MgO,CaO or rare-earth oxide

Supported nickel catalysts prepared using commercial sintered low surface area porous catalyst carriers (containing SiO₂ and/or Al₂O₃) precoated with MgO, CaO or rare-earth oxide show very much higher activity, selectivity and productivity in methane-to-syngas conversion reactions, than the catalysts prepared using catalyst carriers without any precoating. Among the precoating metal oxides, the best performance is observed for MgO.     

Role of tungsten in supported Pt-W reforming catalysts Part I. Modification of platinum activity and selectivity by addition of tungsten

Bimetallic supported Pt-W catalysts are studied for 3-methylhexane reforming. An increase in the activity and selectivity in aromatization is found for Pt-low W/Al₂O₃ catalysts compared to the classical monometallic Pt/Al₂O₃ catalyst. Changes in activity and selectivity, for bimetallic catalysts, are attributed to tungsten moderator interaction effects between platinum and support which modify the metallic particle sizes. These changes are observed on Pt-high W/Al₂O₃ and Pt-W/SiO₂ catalysts. Superficial carbide formation and modification of the hydrogen chemisorption may be proposed to explain the reactivity of Pt-W catalysts under low hydrogen pressure.     

Preparation of Novel Composite VPO/Fumed Silica Catalyst for Partial Oxidation of n-Butane

By applying fumed SiO₂ and the deposition–precipitation method based on organic medium, the composite VPO/fumed SiO₂ catalysts were first prepared and tried for partial oxidation of n-butane to maleic anhydride. In the temperature range of 653–693 K the fumed SiO₂-based catalysts not only showed good activity but also maintained sufficiently high MA selectivity in comparison to some conventional supported VPO catalysts. As an example, the catalyst with 30% VPO content showed butane conversion of 60% and MA selectivity of 58 mol% at 673 K. The turnover rates of low loading samples are found to be higher than that of high loading sample as well as unsupported catalyst. Besides the unique interaction which may exist between VPO component and the fumed SiO₂ material, co-existence of dominant (VO)₂P₂O₇ and minor VOPO₄ in these non-equilibrated catalysts may be favorable for MA formation. Moreover, introducing the additive of polyethylene glycol (PEG) in the preparation medium can obviously enhance the dispersion of VPO component and hence lead to a more selective catalyst.     

Synthesis of diethyl carbonate from dimethyl carbonate and ethanol using KF/Al2O3 as an efficient solid base catalyst

Diethyl carbonate, an efficient oxygen-containing fuel additive was synthesized from dimethyl carbonate and ethanol using KF/Al₂O₃. The catalysts prepared with different KF loading were characterized using X-ray diffraction, BET surface area and basicity measurement analyses. The effects of different reaction parameters such as temperature, reactant ratio and amount of catalyst were optimized. Among the different alkali halides, 20 wt.% KF supported on alumina exhibited 61.6% diethyl carbonate selectivity with 96% dimethyl carbonate conversion under optimum reaction conditions. The plausible reaction mechanism is proposed based on the results obtained. The possibility of recycling the catalyst was ensured without appreciable loss in activity for four cycles.     

Hydrogen Production from Partial Oxidation and Steam Reforming of N‐octane Over Alumina‐supported Ni and Ni‐Pd Catalysts

Hydrogen production by partial oxidation and steam reforming (POSR) of n‐octane was investigated over alumina‐supported Ni and Ni‐Pd catalysts. It showed that Ni‐Pd/Al₂O₃ had higher activity and hydrogen selectivity than the nickel catalyst under the experimental conditions, which indicated Ni‐Pd/Al₂O₃ could be an effective catalyst for the production of hydrogen from hydrocarbons.     

Dibenzothiophene HDS Over Sulphided CoMo on High‐Silica USY Zeolites

USY faujasites (SiO₂/Al₂O₃ = 12, 30 and 80) were used as hydrodesulphurization (HDS) catalyst supports. Mo, Co and P were impregnated at two concentrations: ～12.5, ～3 and ～1.6 mass %; ～18, ～5.5 and ～2.2 mass % (CL and HL series, respectively). Surface acidity decreased after Co‐Mo‐P deposition. Sulphided catalysts were tested in dibenzothiophene (DBT) HDS (320°C, 5.59 MPa). The HDS rate slightly increased with both SiO₂ content and Co‐Mo‐P loading. High selectivity to hydrogenated products suggested deficient Mo promotion in CL solids. Improved Mo promotion by Co (HL series) could be responsible for higher activity and marked selectivity to desulphurization to biphenyl.     

Characterization of some perovskite oxides based on YBa2Cu3O7 − x in relation to their use in methanol production

The oxidized and weakly reducible perovskite oxide YBa₂Cu₃O_{7 − x} (YBCO) has been prepared as a catalyst, supported on γ‐Al₂O₃. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al₂O₃ or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al₂O₃. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C₂–C₄ hydrocarbons. However the YBCO/γ‐Al₂O₃ catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH₃OH production. © 2000 Society of Chemical Industry     

Characterization of Fischer–Tropsch Cobalt-Based Catalytic Systems (Co/SiO<Subscript>2</Subscript> and Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) by X-ray Diffraction and Magnetic Measurements

Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO₂ and Al₂O₃, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co⁰, CoO, Co₃O₄, Co²⁺) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO₂ catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al₂O₃ catalysts. Conversely the Al₂O₃ supported catalysts gave much higher selectivity towards olefins than Co/SiO₂. These results yield the correlation that the presence of Co₃O₄ yield higher methane selectivity whereas the presence of Co²⁺ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.     

Kinetic modeling of heavy reformate conversion into xylenes over mordenite-ZSM5 based catalysts

Conversion of commercial heavy reformate into xylenes is investigated in a fluidized-bed batch reactor to develop a kinetic model. H-mordenite and H-ZSM5 based catalysts containing equal amounts of H-mordenite and H-ZSM-5 (SiO₂/Al₂O₃ ratio: 27) were used. The SiO₂/Al₂O₃ ratio of H-mordenite in the catalysts was 18 and 180, which are named as MLZ and MHZ, respectively. The MLZ catalyst resulted in higher conversion of methylethylbenzenes (MEBs) and trimethylbenzenes (TMBs) and exhibited better selectivity toward xylenes due to higher acid-site concentration. Kinetic modeling was carried out using a simplified reaction network which includes: (i) dealkylation of MEBs; (ii) disproportionation of TMBs; (iii) transalkylation of TMBs with toluene; and (iv) paring reaction of tetramethylbenzenes. The results of the mathematical model closely match the experimental data, based on statistically significant estimate of the kinetic parameters, which indicates that the set of assumptions made for kinetic modeling are valid. The order of apparent activation energies, E_paring ? E_dealkylation = E_{disproportionation} > E_{transalkylation}, can be ascribed to the relative size of the reactant molecules involved in these reactions.     

Role of organic nitro compounds in selective reduction of NOx with ethanol over different supported silver catalysts

The adsorption of organic nitro compounds such as nitromethane and nitroethane on different supported silver catalysts (Ag/Al₂O₃, Ag/TiO₂, Ag/SiO₂) has been studied using infrared spectroscopy. The adsorbed NCO species formation was strongly influenced by the catalyst support and therefore clearly detected on Ag/Al₂O₃ and Ag/TiO₂ catalysts by thermal decomposition of nitromethane and nitroethane at temperatures higher than 150°C. With the Ag/SiO₂ catalyst, very little NCO formation was observed at 350°C. On the other hand, the catalyst support was found to affect the N₂ formation in the selective reduction of NO_x on supported silver catalysts. On the basis of these findings, the role of adsorbed nitromethane, nitroethane and isocyanate species in the selective reduction of NO_x is discussed with respect to the catalyst support effect and the catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.