Aqueous-Phase Hydrogenolysis of Glycerol to 1,3-propanediol Over Pt-H<Subscript>4</Subscript>SiW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Abstract  

Hydrogenolysis of glycerol to 1,3-propanediol in aqueous-phase was investigated over Pt-H₄SiW₁₂O₄₀/SiO₂ bi-functional catalysts with different H₄SiW₁₂O₄₀ (HSiW) loading. Among them, Pt-15HSiW/SiO₂ showed superior performance due to the good dispersion of Pt and appropriate acidity. It is found that Br?nsted acid sites facilitate to produce 1,3-PDO selectively confirmed by Py-IR. The effects of weight hourly space velocity, reaction temperature and hydrogen pressure were also examined. The optimized Pt-HSiW/SiO₂ catalyst showed a 31.4% yield of 1,3-propanediol with glycerol conversion of 81.2% at 200 °C and 6 MPa.     

Direct conversion of cellulose into polyols or H2 over Pt/Na(H)-ZSM-5

The direct conversion of cellulose into polyols such as ethylene glycol and propylene glycol was examined over Pt catalysts supported on H-ZSM-5 with different SiO₂/Al₂O₃ molar ratios. The Pt dispersion, determined by CO chemisorption and transmission electron microscopy (TEM), as well as the surface acid concentration measured by the temperature-programmed desorption of ammonia (NH₃-TPD), increased with decreasing SiO₂/Al₂O₃ molar ratio for Pt/H-ZSM-5. The total yield of the polyols, i.e., sorbitol, manitol, ethylene glycol and propylene glycol, generally increased with increasing Pt dispersion in Pt/H-ZSM-5. The one-pot aqueous-phase reforming of cellulose into H₂ was also examined over the same catalysts. The Pt catalyst supported on H-ZSM-5 with a moderate SiO₂/Al₂O₃ molar ratio and a large external surface area showed the highest H₂ production rate. The Pt dispersion, surface acidity, external surface area and surface hydrophilicity appear to affect the catalytic activity for this reaction.     

聚四氟乙烯修饰的MCM-49分子筛上的正十二烷催化裂解反应

制备MCM-49分子筛负载不同量的聚四氟乙烯催化剂,运用XRD、NH3- TPD和DSA等方法对催化剂表面性能进行表征,并将催化剂应用于正十二烷的催化裂解反应.结果表明,负载聚四氟乙烯后,MCM -49分子筛催化荆表面疏油性得到明显改善,催化剂适当的表面疏油性对于抑制裂解过程中的小分子聚合、阻止积炭的产生和延长催化剂寿...     

Effect of H2 partial pressure on surface reaction parameters during CO hydrogenation on Ru-promoted silica-supported Co catalysts

Steady-state isotopic transient kinetic analysis (SSITKA), one of the most powerful techniques for the investigation of surface reactions, was used to study the effect of hydrogen partial pressure on the fundamental surface reaction parameters for methanation on ordered mesoporous silica (MCM-41) and amorphous SiO₂-supported CoRu catalysts. The abundances, coverages, and lifetimes of surface intermediates of the reaction were measured under reaction conditions and their dependence upon hydrogen partial pressure was determined. Although absolute hydrogen coverage under reaction conditions is not measurable due to the hydrogen isotope effect, relative hydrogen surface concentration as a function of P_H2 could be estimated from SSITKA parameters. Increasing the hydrogen partial pressure at a constant reaction temperature of 220 °C not only caused the expected increase in the relative surface concentration of hydrogen but also increased the abundance of surface methane intermediates (N_M), possibly due to increased hydrogenation. The impact of P_H2 on N_M for MCM-41-supported CoRu catalysts was similar to that for SiO₂-supported ones, showing an approximately twofold increase in N_M as P_H2 increased from 0.23 to 1.71 bar. The relative concentration of surface hydrogen, however, increased fourfold. The abundance of surface methane intermediates and the surface coverages were significantly higher for the MCM-41-supported CoRu catalysts. The average surface reaction residence time of the methane intermediates (τ_M) consistently decreased with increasing hydrogen partial pressure due to the fact that the pseudo first order rate constant (1/τ_M) contains the hydrogen surface concentration term. There was no difference, however, in the intrinsic site activity since the average surface reaction residence times of methane intermediates (τ_M) for SiO₂- and MCM-41-supported CoRu catalysts were essentially identical for a given partial pressure of hydrogen, regardless of Co loading. This also indicates that the type of silica support used (amorphous SiO₂ or MCM-41) did not have an impact on surface hydrogen concentration, contrary to the case for H₂ chemisorption at 100 °C. The increase in rate with increasing hydrogen partial pressure resulted due to the increase in methane surface intermediates and, more importantly, the increase in hydrogen surface concentration.     

Noble metal catalysed aerial oxidation of alcohols to aldehydes in supercritical carbon dioxide

Platinum and palladium supported on carbons are shown to be excellent catalysts for selective oxidation of organic alcohols to aldehydes (>99%) at high yields using dioxygen as an oxidant in supercritical CO₂ fluid medium. There is no detectable over-oxidation of the product to acid and no metal leaching that are commonly encountered in the conventional aqueous medium. It is also found that the hydrophobicity/hydrophilicity of the catalyst surface relative to the CO₂ solvent plays a crucial role in the resulting catalytic activity and stability. Adding 1% Teflon onto the noble metal–carbon catalysts dramatically enhances the activity and lifetime of the catalysts during the aerial oxidation of fine chemicals in scCO₂ fluid.     

Selective oxidation of isobutane to methacrolein over MoVTe mixed oxide supported on SBA-3 and SiO2

SBA-3 and SiO₂-supported MoVTe mixed oxide catalysts have been prepared by impregnation and/or direct synthesis methods and tested for selective oxidation of isobutane to methacrolein (MAL). It was found that the supported catalysts showed much higher activity than the bulk MoVTe mixed oxide for the reaction. Among the supported catalysts, better isobutane conversion and MAL yield were achieved on the 3% MoV_0.8Te_0.23O_x/SBA-3 catalyst prepared by the impregnation method. The catalysts were characterized with BET, XRD, Raman, H₂-TPR, XPS and FT-IR of pyridine adsorption. The good performance of the SiO₂ and SBA-3 supported MoV_0.8Te_0.23O_x catalysts was attributed to a combination of different properties: (i) formation of well dispersed active phases on large surface areas of SiO₂ and SBA-3 supports, which is beneficial for the isolation of active site and preventing the further oxidation of unstable reaction intermediate as well as product; (ii) improved activity for hydrogen abstraction of C-H bond of isobutane due to the formation of isolated pseudotetrahedral VO₄ species.     

Liquid‐phase hydrogenation of cinnamaldehyde over Cu‐Au/SiO2 catalysts

The synthesis, characterization, and application of silica‐supported Cu‐Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu‐Au/SiO₂ bimetallic catalysts were superior to monometallic Cu/SiO₂ and Au/SiO₂ catalysts under identical conditions. Adding a small amount of gold (6Cu‐1.4Au/SiO₂ catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO₂ along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x‐ray diffraction, H₂ temperature‐programmed reduction, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier‐transform infrared spectra of chemisorbed CO, and x‐ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu‐Au/SiO₂ catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H₂ molecules, and Cu⁰ and Cu⁺ sites contributed to the adsorption‐activation of C?C and C?O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au‐Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3300–3311, 2014     

Organometallics derived (Pd + Ln)/SiO2 catalysts for the reactions of synthesis gas conversion

C₃H₆ hydroformylation and CH₃OH synthesis on organometallics derived (Pd + Ln)/ SiO₂ and Pd/SiO₂ catalysts have been studied. The activity and selectivity towards methanol in CO + H₂ reaction were observed to increase for all the modified catalysts while both the hydroformylation activity and selectivity towards oxygenates in C₃H₆ hydroformylation decreased for the catalysts in comparison to those of Pd/SiO₂. The FTIR, TPD data and characteristic catalytic properties of the catalysts studied allow to suggest that C₃H₆ hydroformylation on (Pd + Ln)/SiO₂ catalysts occurs on monometallic Pd clusters without participation of mixed active sites and CO complexes activated thereon.     

Kinetics of Selective Oxidation of Dimethyl Ether to Formaldehyde Over Al2O3-Supported VO x and MoO x Catalysts

The object of this work is to study the effect of hydrothermal treatment on the TS-1/SiO₂ catalyst in propylene epoxidation in fixed bed. The TS-1/SiO₂ catalysts before and after hydrothermal treatment were characterized by means of XRD, XRF, BET, UV–Vis and EPR techniques. It was found by EPR characterization that two types of Ti(IV)-superoxide radicals, A (g _z = 2.0271; g _y = 2.0074; g _x = 2.0010) and B (g _z = 2.0247; g _y = 2.0074; g _x = 2.0010), were observed for the TS-1/SiO₂ catalyst. The superoxo species A was converted to B after the TS-1/SiO₂ catalyst was hydrothermally treated. The results show that hydrothermal treatment temperature and time have marked effects on the activity and the PO selectivity. The optimal hydrothermal treatment temperature and time are 170 and 4 h, respectively. In the long-term propylene epoxidation reaction, about 95% H₂O₂ conversion and above 94% PO selectivity are obtained over TS-1/SiO₂ catalyst hydrothermally treated at 170° C for 4 h.     

Silica-Supported Heteropoly Acids Promoted by Pt/Al2O3 for the Isomerization of n-Hexane

Silica-supported heteropoly acids promoted by Pt/Al₂O₃ present efficient catalytic activity for the isomerization of n-hexane, and among them 50 wt% HSiW/SiO₂ promoted by Pt/Al₂O₃ shows the best catalytic performance, which might be closely related to the maintenance of the surface structure of heteropoly acids during reaction.     

Influence of catalyst pretreatment on catalytic properties and performances of Ru–Re/SiO2 in glycerol hydrogenolysis to propanediols

Bimetallic Ru–Re/SiO₂ and monometallic Ru/SiO₂ catalysts were prepared by impregnation method and their catalytic performances were evaluated in the hydrogenolysis of glycerol to propanediols (1,2-propanediol and 1,3-propanediol) with a batch type reactor (autoclave) under the reaction conditions of 160 °C, 8.0 MPa and 8 h. Ru–Re/SiO₂ showed much higher activity in the hydrogenolysis of glycerol than Ru/SiO₂, and the pretreatment conditions of the catalyst precursors had great influence on the catalytic performance of both Ru–Re/SiO₂ and Ru/SiO₂ catalysts. The physicochemical properties of Ru–Re/SiO₂ and Ru/SiO₂, such as specific surface areas, crystal phases, morphologies/microstructures, surface element states, reduction behaviors and dispersion of Ru metal, were characterized by N₂ adsorption/desorption, XRD, Raman, TEM–EDX, XPS, H₂-TPR and CO chemisorption. The results of XRD, TEM–EDX and CO chemisorption characterizations showed that Re component had an effect on promoting the dispersion of Ru species on the surface of SiO₂, and the measurements of H₂-TPR revealed that the co-existence of Re and Ru components on SiO₂ changed the respective reduction behavior of Re or Ru alone. High pre-reduction temperatures would decrease the activities of Ru–Re/SiO₂ and Ru/SiO₂ catalysts, compared with the corresponding calcined catalysts (without pre-reduction), which actually went through an in-situ reduction during the reaction. XPS analysis indicated that Ru species was in Ru⁰ metal state, while Re species was mostly in Re oxide state in the spent Ru–Re/SiO₂ sample. Re component was probably in rhenium oxide state rather than Re⁰ metal state to take part in the reaction via interaction with Ru⁰ metal.     

Influence of H4SiW12O40 loading on hydrocracking activity of non-sulfide Ni-H4SiW12O40/SiO2 catalysts

The effect of H₄SiW₁₂O₄₀ loading on the catalytic performance of the reduced Ni-H₄SiW₁₂O₄₀/SiO₂ catalysts for hydrocracking of n-decane with or without the presence of thiophene and pyridine is studied. The catalysts were characterized by BET, XRD, Raman, XPS, H₂-TPR, H₂-TPD, NH₃-TPD and FT-IR of pyridine adsorption. It was found that addition of H₄SiW₁₂O₄₀ to the system increases the catalytic activity and the promoting effect is a function of the H₄SiW₁₂O₄₀ loading. The best result was obtained on 5%Ni-50%H₄SiW₁₂O₄₀/SiO₂ catalyst which shows the highest activity for hydrocracking of n-decane and excellent tolerance to the sulfur and nitrogen compounds in the feedstock. The results showed that a suitable amount of H₄SiW₁₂O₄₀ loading on the 5%Ni/SiO₂ catalyst increases the amount of both hydrogen adsorbed and Brønsted acid and Lewis acid sites on the catalyst. The high catalytic performance of the catalyst can be related to the nature of H₄SiW₁₂O₄₀ and the proper balance between metal and acid functions.     

Hydrogenation of Levulinic Acid Using Formic Acid as a Hydrogen Source over Ni/SiO2 Catalysts

Several Ni/SiO₂ catalysts were developed for the hydrogenation of levulinic acid using formic acid as the hydrogen source. The catalysts were prepared by a variety of methods including impregnation, co‐precipitation, deposition‐precipitation, and citric acid assisted impregnation combustion. The morphological properties were investigated by XRD, N₂ sorption, HRTEM, and H₂ pulse chemisorption measurements. XRD patterns of the calcined material revealed the presence of NiO particles, while calcination in an inert atmosphere produced Ni particles through in situ reduction of NiO. The reaction proceeded without external H₂ flow using formic acid as hydrogen source. The Ni/SiO₂ catalyst prepared by the citric acid assisted method and calcined in inert gas flow was the most efficient for the hydrogenation of levulinic acid without external H₂ flow. The high catalytic performance was attributed to the high dispersion of cheap and earth‐abundant Ni nanoparticles and optimal porosity.     

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.     

Selective Hydrogenation of Soybean Oil on Copper Catalysts as a Tool Towards Improved Bioproducts

The liquid-phase soybean oil hydrogenation was studied on silica-supported Cu and ternary Cu–Zn–Al catalysts. Cu/SiO₂ samples were prepared by incipient-wetness impregnation (Cu/SiO₂-Imp) and chemisorption-hydrolysis (Cu/SiO₂-CH), while two Cu–Zn–Al mixed oxides containing 8 (Cu(8)–Zn–Al) and 15?% Cu (Cu(15)–Zn–Al), respectively, were prepared by coprecipitation. Copper dispersion (D _Cu) was 23?% on Cu/SiO₂-CH, and this sample showed a high activity for soybean oil hydrogenation; in contrast, Cu/SiO₂-Imp was inactive, probably because Cu was poorly dispersed (D _Cu?=?2?%). The oil hydrogenation activity on Cu(15)–Zn–Al (D _Cu?=?9?%) was lower than on Cu/SiO₂-CH, while Cu(8)–Zn–Al (D _Cu?=?23?%) was inactive. Citral hydrogenation used as a test reaction showed that the intrinsic Cu⁰ activity was not significantly changed by the kind of support or the catalyst preparation method. These latter results suggested that the observed differences in soybean oil hydrogenation may be explained as changes in accessibility of the triglyceride molecules to Cu active sites. In ternary Cu–Zn–Al samples, access to catalytic sites was hampered by the narrower pore structure of the catalyst. Copper exhibited unique properties for obtaining proper lubricants from soybean oil hydrogenation because selectively hydrogenated unsaturated linolenic (C18:3) and linoleic (C18:2) fatty acids to unsaturated oleic acid (C18:1) without forming saturated stearic acid (C18:0).     

吡啶改性Pd/SiO2催化剂用于H2和O2直接合成H2O2

引言过氧化氢(H2O2)是一种理想的绿色氧化剂,广泛应用于化学品合成、纺织、造纸、环保、食品、医药、冶金和农业等领域[1]。目前,蒽醌法[2-5]是工业上生产H2O2的主要方法。20世纪40年代,德国I.G.Farbenindustrie首先采用蒽醌法(又称Riedl-Pfleiderer法)工业化生产过氧化氢。该方法首先将2-烷基蒽醌(通常是2-乙基蒽醌)溶解于合适的有机溶剂中,溶液中的2-烷基蒽醌经催化剂催化加氢,被还原成蒽氢醌或5,6,7,8-四氢蒽氢醌,再经空气氧化得到蒽醌或四氢蒽醌和     

The Synergy of the Support Acid Function and the Metal Function in the Catalytic Hydrodeoxygenation of m-Cresol

The hydrodeoxygenation (HDO) of m-cresol is investigated as a model for the HDO of phenolic compounds from lignin pyrolysis. Pt catalysts supported on ??-Al₂O₃ and SiO₂ are effective for the conversion of m-cresol to toluene and methylcyclohexane at 533?K and 0.5?atm H₂. Experiments using Pt/??-Al₂O₃ show that the reaction proceeds by a combination of Pt-catalyzed hydrogenation and acid-catalyzed dehydration reactions. Dehydration of a partially hydrogenated oxygenate intermediate is most likely the dominant reaction pathway to toluene. The acidity of the ??-Al₂O₃ support was modified by base (K₂CO₃) and acid (NH₄F) treatments, and increasing the number and strength of acid sites was found to increase the rate of HDO. Pt/SiO₂ was more active for m-cresol HDO than Pt/Al₂O₃. The reaction rate on Pt/Al₂O₃ and Pt/SiO₂ decreased after 5?h on stream, but Pt/Al₂O₃ regained initial reactivity after reductive treatment in H₂.     

Fischer-Tropsch synthesis: Support and cobalt cluster size effects on kinetics over Co/Al2O3 and Co/SiO2 catalysts

The influence of support type and cobalt cluster size (i.e., with average diameters falling within the range of 8-40 nm) on the kinetics of Fischer-Tropsch synthesis (FT) were investigated by kinetic tests employing a CSTR and two Co/γ-Al₂O₃ catalysts having different average pore sizes, and two Co/SiO₂ catalysts prepared on the same support but having different loadings. A kinetic model that contains a water effect constant “m” was used to fit the experimental data obtained with all four catalysts. Kinetic parameters suggest that both support type and average Co particle size impact FT behavior. Cobalt cluster size influenced kinetic parameters such as reaction order, rate constant, and the water effect parameter. In the cluster size range studied, decreasing the average Co cluster diameter by about 30% led to an increase in the intrinsic reaction rate constant k, defined on a per g of catalyst basis, by 62-102% for the γ-Al₂O₃ and SiO₂-supported cobalt catalysts. This increase was due to the higher active Co⁰ surface site density as measured by hydrogen chemisorption. Moreover, less inhibition by adsorbed CO and greater H₂ dissociation on catalysts having smaller Co particles was suggested by the higher a and lower b values obtained for the measured reaction orders. Interestingly, irrespective of support type, the catalysts having smaller average Co particles were more sensitive to water. Comparing the catalysts having strong interactions between cobalt and support (Co/Al₂O₃) to the ones with weak interactions (Co/SiO₂), the water effect parameters were found to be positive (indicating a negative influence on CO conversion) and negative (denoting a positive effect on CO conversion), respectively. No clear trend was observed for b values among the different supports, but greater a and a/b values were observed for both Al₂O₃-supported Co catalysts, implying greater inhibition of the FT rate by strongly adsorbed CO on Co/Al₂O₃ relative to Co/SiO₂. For both supports, the order on P_CO was always found to be negative (i.e., suggesting an inhibiting effect) and positive for P_H2 for all four catalysts. The order of the reaction on P_H2 was close to 0.5, suggesting that dissociated H₂ is likely involved in the catalytic cycle. Finally, in the limited range of average pore diameters studied (13.5 and 18.2 nm), the average pore size of the Al₂O₃-supported Co catalysts displayed no observable impact on the reaction rate or water effect, suggesting either that the reaction is kinetically controlled, or that the pore size difference was not significant enough to elicit a measurable response.     

Amination of Polyethylene Glycol to Polyetheramine over the Supported Nickel Catalysts

Surface nickel (NiO _x ) species, surface NiAl _x O _y compound, and NiO crystallites are present on the Ni/Al₂O₃ catalysts, and the ratio of these nickel species is dependent on the nickel loading. Surface nickel interacts with the TiO₂ support to form a surface nickel titanate compound (NiTiO _x ) which has a lower reducibility. The weak interaction between the surface nickel and the silica support results in the formation of NiO crystallites on the SiO₂ surface. The Ni/Al₂O₃ and Ni/TiO₂ catalysts contain new surface Lewis acid sites and the amount of surface Lewis acid sites increases with increasing nickel concentration. The Ni/SiO₂ catalysts have no sign of the presence of the surface Lewis acid sites. Only the Ni/Al₂O₃ catalysts have shown the ammonia adsorption at temperature of 200°C. Supported nickel on alumina catalysts possess the highest amination conversion, and the amine yield increases with increasing nickel loading up to 15% and starts to level off. By comparing amination catalysis with quantitatively TPR studies of the H₂ consumed of the Ni/Al₂O₃ catalysts, it appears that the dispersed nickel species are the active sites for amination. In addition, the amination product is mainly the secondary amine due to the presence of water.     

Support and additive effects in the synthesis of methanol over copper catalysts

Catalysts containing copper and ZnO in various combinations have been prepared, the copper surface areas have been measured by nitrous oxide frontal chromatography, and the activities in the reaction of CO/CO₂/H₂ and CO/H₂ mixtures to methanol have been determined at 250°C and 10 bar pressure. The results show that there is a strong synergy between copper and ZnO with the area specific rate of Cu/ZnO catalysts being about one order of magnitude larger than that of a Cu/SiO₂ catalyst. The synergy between copper and ZnO is observed both in the presence and absence of carbon dioxide. It is also observed that physical mixtures of Cu/SiO₂ and ZnO/SiO₂ catalysts are significantly more active than either of the components alone. The results are discussed in terms of possible interactions between copper and ZnO in the most active catalysts.