Liquid fuel production from syngas using bifunctional CuO-CoO-Cr2O3 catalyst mixed with MFI zeolite

CuO-CoO-Cr₂O₃ mixed with MFI Zeolite (Si/Al = 35) prepared by co-precipitation was used for synthesis gas conversion to long chain hydrocarbon fuel. CuO-CoO-Cr₂O₃ catalyst was prepared by co-precipitation method using citric acid as complexant with physicochemical characterization by BET, TPR, TGA, XRD, H₂-chemisorptions, SEM and TEM techniques. The conversion experiments were carried out in a fixed bed reactor, with different temperatures (225-325 °C), gas hourly space velocity (457 to 850 h⁻¹) and pressure (28-38 atm). The key products of the reaction were analyzed by gas chromatography mass spectroscopy (GC-MS). Significantly high yields of liquid aromatic hydrocarbon products were obtained over this catalyst. Higher temperature and pressure favored the CO conversion and formation of these liquid (C₅-C₁₅) hydrocarbons. Higher selectivity of C₅ + hydrocarbons observed at lower H₂/CO ratio and GHSV of the feed gas. On the other hand high yields of methane resulted, with a decrease in C₅+ to C₁₁+ fractions at lower GHSV. Addition of MFI Zeolite (Si/Al = 35) to catalyst CuO-CoO-Cr₂O₃ resulted a high conversion of CO-hydrogenation, which may be due to its large surface area and small particle size creating more active sites. The homogeneity of various components was also helpful to enhance the synergistic effect of Co promoters.     

Catalytic conversion of syngas into C2 oxygenates over Rh-based catalysts—Effect of carbon supports

Ethanol is considered as a potential alternative synthetic fuel to be used in automobiles or as a potential source of hydrogen for fuel cells. In this paper we first undertake a brief overview of the catalyst development for syngas conversion to C₂ oxygenates over Rh-based catalysts, mainly on the effects of various additives and supports on the activity and selectivity. Then we investigated the effects of carbon materials, which have been rarely studied as supports for Rh-based catalysts in this process. For example, rather well graphitized carbon black, very high surface area CMK-3 and activated carbon (AC) were compared to carbon nanotubes (CNTs), which exhibits a medium level surface area with well defined nanochannels. The CNT-supported catalyst shows a highest overall activity and yield of C₂ oxygenates compared to the other carbon-supported catalysts. The catalysts are characterized by N₂ adsorption–desorption, CO chemisorption, TEM, XRD and TPD. The graphitized structure combined with the tubular morphology of CNTs likely play an important role.     

Catalysis in C1 chemistry: Future and prospect

This work summarizes the most relevant facets of the current knowledge of the principal catalytic processes involved in one carbon-atom conversions. Without doubt, natural gas (or methane) chemical conversion into high molecular weight hydrocarbons via oxidative coupling (OCM) or partial oxidation into C₁ oxygenates (POM) currently represents a great chemical and technological challenge for petrochemistry. Although the catalyst systems and the basic principles of the two types of processes are well known, a greater effort is needed towards the development of more efficient and stable catalysts under the severe operation conditions imposed by the reaction itself, as well as the need for suitable reaction design to minimize the extent of the homogeneous reaction. The alternative process is to obtain synthesis gas (CO/H₂) in a first step through steam reforming followed by a second Fischer-Tropsch hydrogenation step. However, the unfavorable energetic balance of the reforming step and the absence of selective catalysts in the latter to obtain a narrow molecular weight distribution currently leads to compromise in solutions. Among these, the high molecular weight alcohol synthesis and the recently developed Shell middle distillate synthesis (SMDS) appear to be very attractive. Of no less importance are the reactions which incorporate a CO molecule into alcohols or olefins via carbonylations and hydroformylations. Within this framework, the use of organometallic complexes anchored to functionalized polymeric matrices initiated a very intense research activity, particularly in the development of stable catalysts.     

Selective oxidation of methane to methanol and formaldehyde over V2O5/SiO2 catalysts. Role of NO in the gas phase

The role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C₂-hydrocarbons and C₂-oxygenates is evaluated. The addition of NO increases the conversion of methane under all the experimental conditions studied and has a strong effect on the product distribution. At low NO concentration the catalysts yield mainly C₂H_n hydrocarbons, but at higher NO concentrations, carbon oxides dominate. Amongst the C₁-oxygenates produced, methanol is the major compound observed and its proportion increases with increasing NO concentration. The highest C₁-oxygenates yield was 7% at atmospheric pressure. This revised version was published online in July 2006 with corrections to the Cover Date.     

CO hydrogenation over a RhVO4/SiO2 catalyst after H2 reduction

The hydrogenation of CO over a RhVO₄/SiO₂ catalyst has been investigated after H₂ reduction at 773 K. A strong metal–oxide interaction (SMOI) induced by the decomposition of RhVO₄ in H₂ enhanced not only the selectivity to C₂ oxygenates but also the CO conversion drastically, compared with an unpromoted Rh/SiO₂ catalyst. The selectivity of the RhVO₄/SiO₂ catalyst was similar to those of conventional V₂O₅‐promoted Rh/SiO₂ catalysts (V₂O₅–Rh/SiO₂), but the CO dissociation activity (and TOF) was much higher than for V₂O₅–Rh/SiO₂, and hence the yield of C₂ oxygenates was increased. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-temperature catalytic combustion of methane over MnO x –CeO2 mixed oxide catalysts: Effect of preparation method

The effect of preparation method on MnO _x –CeO₂ mixed oxide catalysts for methane combustion at low temperature was investigated by means of BET, XRD, XPS, H₂-TPR techniques and methane oxidation reaction. The catalysts were prepared by the conventional coprecipitation, plasma and modified coprecipitation methods, respectively. It was found that the catalyst prepared by modified coprecipitation was the most active, over which methane conversion reached 90% at a temperature as low as 390 °C. The XRD results showed the preparation methods had no effect on the solid solution structure of MnO _x –CeO₂ catalysts. More Mn⁴⁺ and richer lattice oxygen were found on the surface of the modified coprecipitation prepared catalyst with the help of XPS analysis, and its reduction and BET surface area were remarkably promoted. These factors could be responsible for its higher activity for methane combustion at low temperature.     

Size Dependent Study of MeOH Decomposition Over Size-selected Pt Nanoparticles Synthesized via Micelle Encapsulation

We communicate experimental results for the oxidation of methane by oxygen over alumina supported Pd and Pt monolith catalysts under transient conditions. Temperature programmed reaction (TPReaction) and reactant pulse-response (PR) experiments have been performed, using a continuous gas-flow reactor equipped with a downstream mass spectrometer for gas phase analysis. Special attention was paid to the influence of gas composition changes, i.e., O₂ and H₂ pulsing, respectively, on the methane conversion. For Pt/Al₂O₃ oxygen pulsing can significantly increase the methane conversion which can be even further improved by pulsing hydrogen instead. Such transient effects are not observed for the Pd/Al₂O₃ catalyst for which instead constantly lean conditions is beneficial. Our results suggest that under lean conditions Pd and Pt crystallites may undergo bulk- and partial (surface oxide formation) oxidation, respectively, which for Pd results in more active surfaces, while for Pt the activity is reduced. The latter seems to connect to a lowering of the ability to dissociate methane.     

Selective synthesis of C2-C4 hydrocarbons from CO + H2 on composite catalysts

A copper-zinc-aluminum methanol synthesis catalyst has been prepared using a precipitated hydrotalcite-type precursor that decomposes to a mixture of the corresponding amorphous oxides at a low temperature. TPR studies show that such a mixture is easy to reduce giving a highly dispersed catalyst. When this is mixed with a zeolite, the resulting hybrid catalyst gives C₂-C₄ hydrocarbons with very high selectivity. This may be useful in obtaining LPG from synthesis gas.     

Structure and Reactivity of sol–gel V/SiO<Subscript>2</Subscript> Catalysts for the Direct Conversion of Methane to Formaldehyde

Vanadium oxide-silica catalysts prepared by the sol–gel method were characterized by different techniques (nitrogen adsorption–desorption isotherms, scanning electron microscopy, X-ray diffraction, temperature-programmed reduction, Raman spectroscopy and X-ray photoelectron spectroscopy) and applied in the direct conversion of methane to C1 oxygenates. The addition of a small amount of nitric oxide to the reaction mixture reduced the energy barrier for H-abstraction, increasing the methane conversion and formaldehyde yield. Correlations between the characterization and activity results indicate that the reaction occurs on tetrahedrally coordinated vanadium sites, as the maximum formaldehyde yield was found for the catalyst with a vanadium content of 1.5 wt%, which has a high surface density of well-dispersed tetrahedrally coordinated monomeric or slightly oligomerized VO₄ species. On the other hand, a high space velocity and CH₄:O₂ ratio decrease the subsequent oxidation to carbon oxides, increasing oxygenate formation.     

Conversion of methane to higher hydrocarbons in pulsed DC barrier discharge at atmospheric pressure

Conversion of methane to C₂/C₃ or higher hydrocarbons in a pulsed DC barrier discharge at atmospheric pressure was studied. Non-equilibrium plasma was generated in the barrier discharge reactor. In this plasma, electrons which had sufficient energy collided with the molecules of methane, which were then activated and coupled to C₂/C₃ or higher hydrocarbons. The effect of the change of applied voltage, pulse frequency and methane flow rate on methane conversion, selectivities and yields of products was studied. Methane conversion to higher hydrocarbons was about 25% as the maximum. Ethane, propane and ethylene were produced as primary products, including a small amount of unidentified C₄ hydrocarbons. The selectivity and yield of ethane as a main product came to about 80% and 17% as the highest, respectively. The selectivities of ethane and ethylene were influenced not by the change of pulse frequency but by the change of applied voltage and methane flow rate. However, in case of propane, the selectivity was independent of those condition changes. The effect of the packing materials such as glass and A1₂O₃ bead on methane conversion was also considered, showing that A1₂O₃ played a role in enhancing the selectivity of ethane remarkably as a catalyst.     

Ambient temperature oxidation of carbon monoxide using a Cu2Ag2O3 catalyst

The mixed copper–silver oxide, Cu₂Ag₂O₃, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu₂Ag₂O₃, aged for 4 h was at least as active as the hopcalite.     

Promoting Effect of Pt Addition to V2O5/ZrO2 Catalyst on Reduction of NO by C3H6

The effect of Pt addition to a V₂O₅/ZrO₂ catalyst on the reduction of NO by C₃H₆ has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C₃H₆ reaction through a reduction–oxidation cycle between its oxide and cluster form.     

CH4-CO2 reforming over Ni/Al2O3 aerogel catalysts in a fluidized bed reactor

Ni/Al₂O₃ aerogel catalysts were synthesized by a sol-gel method combined with a supercritical drying route. The catalytic performances of the catalysts in methane reforming with CO₂ were investigated in a quartz micro-reactor. The results indicated that the aerogel catalyst showed higher specific surface area and higher dispersivity of nickel species than those of impregnation catalyst. The excellent catalytic performances and stabilities were achieved over the aerogel catalysts in the fluidized bed reactor. Comprehensive characterization with TG, XRD and FESEM revealed that the aerogel catalyst in the fluidized bed had much lower carbon deposition than that in the fixed bed. The fluidization of the aerogel catalyst greatly improved the contact efficiency of gas-solid phase, which accelerated the gasification of the deposited carbon. In contrast, the deactivation of the aerogel catalyst was caused by the carbon deposition due to the catalyst without moving in the fixed bed. Moreover, decreasing activity of the impregnation catalyst in the fluidized bed resulted from the poor fluidization state of catalyst particles and low effective active sites on surface of catalyst.     

NO x -catalyzed partial oxidation of methane and ethane to formaldehyde by dioxygen

At 600 °C, NO_x catalyzes the partial oxidation of both methane and ethane by dioxygen to form formaldehyde. The yield of oxygenates from methane is over 11. The yield increases to over 16 when 0.7% of ethane is added to the gas mixture. The yield of oxygenates from ethane is over 24. A catalytic cycle involving NO₂ as the C–H activating species is proposed.     

Regeneration behaviors of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for C2H6 dehydrogenation with CO2 to C2H4

The catalytic performance of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for conversion of C₂H₆ with CO₂ to C₂H₄ was examined in a continuous‐flow and fixed‐bed reactor. The results show that the Fe–Mn/Si‐2 catalyst exhibits much better reaction activity and selectivity to C₂H₄ than those of the Fe/Si‐2 catalyst. Furthermore, the coking–decoking behaviors of these catalysts were studied through TG. The catalytic performances of the catalysts after regeneration for conversion of C₂H₆ or dilute C₂H₆ in FCC off‐gas with CO₂ to C₂H₄ were also examined. The results show that both activity and selectivity of the Fe–Mn/Si‐2 catalyst after regeneration reached the same level as those of the fresh catalyst, whereas it is difficult for the Fe/Si‐2 catalyst to refresh its reaction behavior after regeneration. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic and electrocatalytic oxidation of propane on V-Mg-O and V-Mg-O (Ag) catalysts

Vanadium magnesium oxide catalysts prepared in this work were found active in selective oxidation of propane to propene. A selectivity as high as 79% was obtained at 10% conversion (813 K). No oxygenated or C₂ products were detected and the catalysts were found to undergo no change in activity over many weeks of operation. Under electrochemical pumping of oxygen (EOP) towards the catalyst (with oxygen present in the feed gas), both conversion and selectivity were found to increase slightly as external current increased, indicating the effect of electrical current can be exhibited by an oxide catalyst. However, in the absence of oxygen in the feed gas, EOP could lead to an even higher selectivity: 84 and 86.9% respectively for a 24 V-Mg-O and a 24 V-Mg-O (Ag) (1/2) catalyst. The overall results obtained suggest that electrochemically supplied oxygen is more selective towards C₃H₆. Mechanisms of both catalytic and electrocatalytic oxidation of propane were tentatively suggested, with surface oxygen ion vacancy identified as active surface species and the rate determining step involving heterolytic splitting of the C₃H₈ molecule to form a surface bonded C₃H ₇ ^– ion and a surface hydroxyl ion. The higher selectivity towards C₃H₆ in case of EOP was explained on this basis. While mixing with Ag powder was found to improve significantly the electrocatalytic performance of vanadium magnesium oxide, its role appears to be non-chemical: it simply gives rise to a larger area of the gas/catalyst/Ag electrode interface.     

Conversion of methane through dielectric-barrier discharge plasma

Methane coupling to produce C₂ hydrocarbons through a dielectric-barrier discharge (DBD) plasma reaction was studied in four DBD reactors. The effects of high voltage electrode position, different discharge gap, types of inner electrode, volume ratio of hydrogen to methane and air cooling method on the conversion of methane and distribution of products were investigated. Conversion of methane is obviously lower when a high voltage electrode acts as an outer electrode than when it acts as an inner electrode. The lifting of reaction temperature becomes slow due to cooling of outer electrode and the temperature can be controlled in the expected range of 60°C–150°C for ensuring better methane conversion and safe operation. The parameters of reactors have obvious effects on methane conversion, but it only slightly affects distribution of the products. The main products are ethylene, ethane and propane. The selectivity of C₂ hydrocarbons can reach 74.50% when volume ratio of hydrogen to methane is 1.50. __________ Translated from Petrochemical Technology, 2007, 36(11): 1099–1103 [译自: 石油化工]     

Oxidative coupling of methane over LaF3/La2O3 catalysts

We studied the oxidative coupling of methane over the LaF₃/La₂O₃ (5050) catalyst. The catalyst was found active even at 873 K. At 1023 K, the C₂ yield was 12.7% at 26.0% CH₄ conversion and 49.1% C₂ selectivity. It was found to be stable and had a lifetime not less than 50 h at 1023 K. The catalyst was effective in C₂H₆ conversion to C₂H₄. XRD results indicated that the catalyst was mainly rhombohedral LaOF. It is suggested that the catalyst has ample stoichiometric defects and generates active oxygen sites suitable for methane dehydrogenation.     

Highly efficient complete oxidation of dilute benzene over ultrafine Cu0.1Ce0.5Zr0.4O2−δ catalyst in a fluidized bed reactor

Ultrafine Cu_0.1Ce_0.5Zr_0.4O_2−δ catalyst operated in a fluidized bed reactor was found to be very effective for complete oxidation of dilute benzene in air. The complete conversion of benzene could be achieved at reaction temperature as low as 220 °C. The mechanism of benzene oxidation over the Cu_0.1Ce_0.5Zr_0.4O_2−δ catalyst was investigated by conducting pulse reaction of pure benzene in the absence of O₂ over the catalyst and the results indicated the involvement of lattice oxygen from the catalyst in benzene oxidation.     

Oxidative coupling of methane over NbO (p-type) and Nb2O5 (n-type) semiconductor materials

Oxidative coupling of methane to higher hydrocarbons was investigated using two types of semiconductor catalysts, NbO (p-type) and Nb₂O₅ (n-type) at 1 atm pressure. The ratio of methane partial pressure to oxygen partial pressure was changed from 2 to 112 and the temperature was kept at 1023 K in the experiments conducted in a cofeed mode. The results indicated a strong correlation between C₂₊ selectivity performance and the electronic properties of the catalyst in terms of p-vs. n-type conductivity. The p-type semiconductor catalyst, NbO, had a larger selectivity (e.g. 95.92%) over the n-type Nb₂O₅ catalyst (23.08%) both at the same methane conversion of 0.64%. Catalyst characterization via X-ray diffraction, TGA and reaction studies indicated that NbO was transformed to Nb₂O₅ during the course of the reaction which limits catalyst life.