Ni-olivine catalysts prepared by thermal impregnation: Structure, steam reforming activity, and stability

Ni-olivine catalysts prepared by thermal impregnation are candidate materials for in-bed catalytic tar removal during fluidized bed biomass gasification. The present work examined the structure and surface properties of the Ni-olivine catalysts prepared by thermal impregnation following preparation, during reduction by in-situ techniques, and following naphthalene-steam reforming in simulated biomass derived syngas. Catalysts were characterized by BET surface area, laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). During the preparation, secondary phases containing Mg (i.e., (Mg,Fe)₃Si₂O₅(OH)₄ and MgFe₂O₄) reacted to form an olivine phase enriched in Mg and either MgO or Mg-enriched (Mg,Ni)O. The presence of excess steam in the naphthalene-steam reforming appeared to limit coking and also caused behavior to be different than was observed under reducing conditions. Post-reaction characterization indicated the loss of a metallic phase through a possible alloying process and the exchange of Fe for Mg in the olivine structure. Either can potentially explain the high coke resistance of the Ni-olivine catalysts prepared by thermal impregnation compared to Ni-olivine catalysts prepared by incipient wetness impregnation or the olivine support. Finally, the properties of the olivine catalysts with and without Ni were compared through activity for methanol- and ethylene-steam reforming.     

Development of Ni catalysts for gas production from biomass gasification. Reactivity in steam- and dry-reforming

Biomass gasification can be optimised in a fluidised bed by the use of metallic nickel as active phase grafted on olivine. Natural olivine ((Mg, Fe)₂SiO₄) has been chosen as catalyst support because of its activity in biomass steam gasification and tar cracking, its high attrition resistance.

After impregnation of nickel oxide on olivine and calcination at 900, 1100 or 1400°C, different interactions between the precursor and the support have been revealed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy coupled to energy dispersive X-ray spectroscopy. Temperature programmed reduction has completed this study and permitted to control the reducibility of the catalysts. The most promising catalyst determined after these different characterisation studies contained 2.8 wt.% of Ni and was calcined at 1100°C. It exhibited strong nickel–olivine interaction but the grafted nickel oxide particles stayed reducible under catalytic test conditions.

Already at 750°C, this catalyst presented a high activity in dry-reforming (95% methane conversion) and steam-reforming (88% methane conversion) and yield in syngas (80% and 75% CO yield, respectively). An excess of water content in steam-reforming inhibited the catalytic activation which could be retrieved by addition of a reducer like H₂.

No sintering of nickel particles and very little carbon deposition has been observed on this catalytic system by characterisation studies after catalytic tests. This can explain its very good ageing behaviour (at least 260 h at 800°C) and justifies its use in a fluidised bed pilot plant.     

The role of the oxidic support on the deactivation of Pt catalysts during the CO2 reforming of methane

Pt supported on γ-Al₂O₃, TiO₂ and ZrO₂ are active catalysts for the CO₂ reforming of methane to synthesis gas. The stability of the catalysts increased in the order Pt/γ-A1₂O₃ < Pt/TiO₂ < Pt/ZrO₂. For all catalysts, the decrease in activity with time on stream is caused by carbon formation, which blocks the active metal sites for reaction. With Pt/TiO₂ and Pt/ZrO₂, deactivation started immediately after the start of the reaction, while the Pt/γ-A1₂O₃ catalyst showed an induction period during which carbon was accumulated without affecting the catalytic activity.     

Transient studies of carbon dioxide reforming of methane over Pt/ZrO2 and Pt/Al2O3

The mechanism of the CO₂ reforming of methane reaction over the Pt/ZrO₂ catalyst was investigated using a temporal analysis of products (TAP) reactor system. For comparative purposes, the reaction pathway using a Pt/Al₂O₃ catalyst was also examined. A reaction sequence is suggested for both catalysts. Over both catalysts, methane decomposition takes place over platinum. The main difference between the two catalysts concerns the carbon dioxide dissociation. Over Pt/Al₂O₃ this step is assisted by hydrogen. Over Pt/ZrO₂ this step takes place over the zirconia support and involves surface vacancies. Moreover, large pools of formate and carbonate species are present on the zirconia. Transient studies conducted to determine the origin of carbon species accumulated during CO₂ reforming revealed that more than 99% of the carbon was derived from the methane molecule over both catalysts. Over the Pt/ZrO₂ catalyst, only a single very reactive carbon species was detected, while over the Pt/Al₂O₃ a second less active species was also formed.     

Light alkanes CO2 reforming to synthesis gas over Ni based catalysts

The CO₂ reforming of methane and propane has been compared over two different Ni catalysts: one reference Ni/SiO₂ system and a Ni/Mg(Al)O hydrotalcite-derived catalyst, shown previously to display high catalytic stability for long term reforming. By combining the Tapered Element Oscillating Microbalance (TEOM), Temperature Programmed Hydrogenation (TPH), Transmission Electron Microscopy (TEM) and magnetic measurements, the formation of coke and its role on the catalyst activity has been investigated and compared for both hydrocarbons. It was found that Ni/SiO₂ and Ni/Mg(Al)O are both more active for methane reforming than for propane reforming. Coke formation is much more pronounced for propane than for methane over both catalysts. However, for both hydrocarbons a much faster carbon formation is observed over the Ni/SiO₂ catalyst than over the Ni/Mg(Al)O catalyst. The difference in the rates of coke formation for methane and propane is ascribed in the case of propane to partially dehydrogenated C₃ adspecies, which are good coke precursors. The superior stability of the hydrotalcite-derived catalyst is due to the strong interaction of the nickel phase with the support and the capacity of the support to activate CO₂ and channel oxygen to the nickel phase.     

A new use of boiler ash: recovery of vanadium as a catalytic VPO system

A VPO system was prepared from boiler-ash. VO(H₂PO₄)₂ phase has been obtained at low temperature and characterized through a combination of techniques including TG-DTA analysis, X-ray powder diffraction and FT-Raman spectroscopy. The thermal decomposition of the precursor material gives a VO(PO₃)₂ and V(PO₃)₃ phase mixture. Supported and unsupported catalysts prepared were compared and contrasted in the partial oxidation of methane (POM). The catalysts were more selective to C₂-hydrocarbons than a VPO catalyst prepared by the conventional method and studied in similar conditions. Thus, the selectivity to C₁-oxygenates was similar, however, the selectivity to CO_x products was hindered. The observation that the precursor VO(H₂PO₄)₂ obtained from boiler ash as recovery and precipitation of the vanadium can generate catalysts of low selectivity to total oxidation products might provide a useful insight into the design of a new series of high activity and high selectivity partial oxidation catalysts.     

Reaction of 4-(naphthylmethyl)bibenzyl, thermally and in the presence of fe ( co )3 ( Pph3 )2

The reaction pathways, kinetics and mechanisms of 4-(naphthylmethyl)bibenzyl (NBBM) have been studied in order to resolve the fundamentals underlying the catalysis of coal liquefaction by Fe-based catalysts. Reactions of NBBM: ( 1 ) under nitrogen in the absence of catalyst, (2) under hydrogen in the absence of catalyst, (3) under nitrogen in the presence of the catalyst precursor Fe(CO)₃(PPh₃)₂, and (4) under hydrogen in the presence of the catalyst precursor Fe(CO)₃(PPh₃)₂ were accomplished. Thermolysis was selective for cleavage of the weak bibenzyl bond, whereas the catalyst precursor effected cleavage at the naphthyl moiety. The catalyst precursor was most effective in the presence of hydrogen, where the rate of consumption of NBBM and the selectivity of breaking the bond at the naphthalene ring both increased. Hydrogenation activity was also observed. Possible mechanisms are proposed to describe the pyrolytic and catalytic reactions of NBBM.     

一种新γ相氧化铝负载的铁铝双金属催化剂用于反向水煤气转化反应(英文)

In reverse water gas shift (RWGS) reaction CO₂ is converted to CO which in turn can be used to produce beneficial chemicals such as methanol. In the present study, Mo/Al₂O₃, Fe/Al₂O₃ and Fe-Mo/Al₂O₃ catalysts were synthesised using impregnation method. The structures of catalysts were studied using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, inductively coupled plasma atomic emission spectrometer (ICP-AES), temperature programmed reduction (H₂-TPR), CO chemisorption, energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques. Kinetic properties of all catalysts were investigated in a batch reactor for RWGS reaction. The results indicated that Mo existence in structure of Fe-Mo/Al₂O₃ catalyst enhances its activity as compared to Fe/Al₂O₃. This enhancement is probably due to better Fe dispersion and smaller particle size of Fe species. Stability test of Fe-Mo/Al₂O₃ catalyst was carried out in a fixed bed reactor and a high CO yield for 60 h of time on stream was demonstrated. Fe₂(MoO₄)₃ phase was found in the structures of fresh and used catalysts. TPR results also indicate that Fe₂(MoO₄)₃ phase has low reducibility, therefore the Fe₂(MoO₄)₃ phase signifificantly inhibits the reduction of the remaining Fe oxides in the catalyst, resulted in high stability of Fe-Mo/Al₂O₃ catalyst. Overall, this study introduces Fe-Mo/Al₂O₃ as a novel catalyst with high CO yield, almost no by-products and fairly stable for RWGS reaction.     

Hydrogen production by catalytic gasification of cellulose in supercritical water

Cellulose, one of the important components of biomass, was gasified in supercritical water to produce hydrogen-rich gas in an autoclave which was operated batch-wise under high-pressure. K₂CO₃ and Ca(OH)₂ were selected as the catalysts (or promoters). The temperature was kept between 450°C and 500°C while pressure was maintained at 24–26 MPa. The reaction time was 20 min. Experimental results showed that the two catalysts had good catalytic effect and optimum amounts were observed for each catalyst. When 0.2 g K₂CO₃ was added, the hydrogen yield could reach 9.456 molkg^-1 which was two times of the H₂ amount produced without catalyst. When 1.6 g Ca(OH)₂ was added, the H₂ yield was 8.265 molkg^-1 which is lower than that obtained using K₂CO₃ as catalyst but is still 1.7 times that achieved without catalyst. Comparing with the results obtained using K₂CO₃ or Ca(OH)₂ alone, the use of a combination of K₂CO₃ and Ca(OH)₂ could increase the H₂ yield by up to 2.5 times that without catalyst and 25% and 45% more than that obtained using K₂CO₃ and Ca(OH)₂ alone, respectively. It was found that methane was the dominant product at relatively low temperature. When the temperature was increased, the methane reacts with water and is converted to hydrogen and carbon dioxide.     

蛇纹石与绿矾耦合提取富镁溶液矿化二氧化碳并回收镍

蛇纹石与绿矾耦合提取镁用于矿化二氧化碳,并富集回收蛇纹石中的镍,这为处理蛇纹石和绿矾提供了一条新的路径。为得到富镁溶液,同时从溶液中分离镍,以蛇纹石与绿矾混合焙烧-浸出后得到的溶液为研究对象,采用水解沉淀法除铁,二乙基二硫代氨基甲酸钠(DDTC)络合法分离镍镁,得到镍的产物和富镁溶液并将其用于二氧化碳矿化。结果表明,该方法能够高效地去除杂质、分离镍镁。在30℃、p H为5.0条件下,铁的去除率达97.36%,而镍、镁的损失率较低。在最佳络合条件下,镍的络合率达到99.50%,而镁的损失率仅为3.03%。此外,对络合机理进行了研究,DDTC中的特征官能团是—SH,络合之后镍和铁分别以Ni[(C₂H₅)₂NCS₂]₂,Fe[(C₂H₅)₂NCS₂]₃的形式存在,而镁不会被络合。富镁溶液在80℃下矿化率达92.63%。每1 000 kg蛇纹石可固定227.38 kg的二氧化碳...     

Low temperature oxidation of methane over Pd/SnO2 catalyst

Catalytic activities of supported Pd were investigated for low temperature oxidation of methane. Pd/SnO₂ catalysts demonstrated excellent activity for methane oxidation in spite of their low surface area. The catalytic activity of Pd/SnO₂ was strongly affected by the preparation procedure. Impregnation of Pd on SnO₂ using aqueous solution of Pd(CH₃COO)₂ was most effective in enhancing the catalytic activity. The catalytic activity was also improved when well-crystallized SnO₂ was employed as a support material. TEM observations revealed that catalytic activity is strongly influenced by the dispersion state of Pd. For the active catalysts, strong interaction between Pd and SnO₂ support was observed in the adsorption of oxygen.     

Multi-metal cyanide catalysts for ring-opening polymerization of propylene oxide

Polymerizations of propylene oxide (PO) have been carried out by using a series of multi-metal metal cyanide (MMC) catalysts prepared by reacting ZnCl₂ and K₃[Co(CN)₆]₂, K₄Fe(CN)₆, K₃Fe(CN)₆ and/or K₂Ni(CN)₄ in the presence of tert-butyl alcohol and polytetramethylene ether glycol as complexing agents. The resulting MMC catalysts are characterized by elemental analysis, X-ray photoelectron spectroscopy, infrared spectroscopy and X-ray powder diffraction. The structure of MMC catalysts with broadened X-ray diffraction peaks is different from that of highly crystalline Prussian blue analogues of microporous crystalline materials due to the coordination of complexing agents. The PO polymerization behavior was tunable by changing with various metal cyanide salts after fixing a main catalyst component as ZnCl₂. Even if the basic structure of the MMC complexes is different each other, i.e. orthorhombic for Zn₂[Fe(CN)₆] and monoclinic for Zn₃[Fe(CN)₆]₂ and Zn₃[Co(CN)₆]₂, the chemical formulations become more complicated by forming MMC complexes through cyano bridges and complexing agents’ coordination and the structure more distorted from the defined crystal structures. All catalysts prepared by using K₃[Co(CN)₆]₂ showed very high activity once they were activated. Simply changing catalyst formulation by choosing different metal cyanide salts, catalytic activity, induction period, polymer molecular weight and its distribution and polymer viscosity could be tuned.     

Water-soluble niobium peroxo complexes as precursors for the preparation of Nb-based oxide catalysts

In the frame of research aimed at developing new synthetic procedures of multimetallic Nb-based catalysts, peroxo complexes of niobium(V) of general formula A^I₃[Nb(O₂)₄] and A^I₃[Nb(O₂)_x(H_yL)]·nH₂O (A^I: NH₄⁺, CN₃H₆⁺ (gu); L: oxalate, tartrate, citrate) have been prepared and characterized on the basis of elemental and thermal analysis, FTIR and ¹³C-NMR spectra. The crystal structure of (gu)₃[Nb(O₂)₄] and (gu)₃[Nb(O₂)₂(C₂O₄)₂]·2H₂O have been determined. The application of the obtained Nb complexes as precursors for the preparation of silica-supported Nb–Mo–O catalysts has been demonstrated. Combining Nb peroxo-carboxylato compounds with analogous Mo(VI) compounds in a silica-impregnation method carried out in aqueous medium leads to the formation of the supported Nb₂Mo₃O₁₄ phase.     

Catalytic combustion of natural gas as the role of on-site heat supply in rapid catalytic CO2---H2O reforming of methane

Development in highly active catalysts for the reforming of methane with H₂O, CO₂, and H₂O+CO₂, and partial oxidation of methane was conducted to produce hydrogen with high reaction rates. A Ni-based three-component catalyst such as Ni---La₂O₃---Ru or Ni---Ce₂O₃---Pt supported on alumina wash-coated ceramic fiber in a plate shape was very suitable for both reactions. The catalyst composition was set at 10 wt.-% Ni, 5.6 wt.-% La₂0₃, and 0.57 wt.-% Ru for example, or molar ratios of these components were 1:0.2:0.03. Even with such a low concentration, the precious metal enhanced the reaction rate markedly, and this synergistic effect was ascribed to the hydrogen spillover effect through the part of precious metal and it resulted in a more reduced surface of the main catalyst component. In particular, a marked enhancement in the reaction rate of CO₂-reforming of methane was observed by the modification of a low concentration Rh to the Ni---Ce₂0₃---Pt catalyst. Very high space-time yields of H₂ (i.e., 8300 mol/1 h in partial oxidation of methane at 600°C with a methane conversion of 37.5%, and 3585 mol/1 h in CO₂reforming of methane at 600°C with a methane conversion of 58%) were realized in those reactions. By combining the catalytic combustion reaction, methane conversion to syngas was markedly enhanced, and even with a very short contact time (10 ms) the conversion of methane increased more than that at 50 ms. The space-time yield of hydrogen amounted to 2,780 mol/1 h with a methane conversion of 90% at 700°C. Furthermore, in a reaction of CH₄---CO₂---H₂O---O₂ on the four components catalyst, an extraordinarily high space-time yield of hydrogen, 12 190 mol/1 h, could be realized under the conditions of very high space velocity (5 ms).     

Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe_2(SO_4)_3 as iron precursor. In addition, as for Fe_2(SO_4)_3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O due to the reduction in Fe_2(MoO_4)_3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO_3 and Fe_2(MoO_4) for FeCl_3·6H_2O and Fe_2(SO_4)_3 as precursors. Iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.     

Hydrodenitrogenation of pyridine over alumina-supported iridium catalysts

The catalytic properties of alumina-supported Ir catalysts (≈1 wt% Ir) were studied in the hydrodenitrogenation (HDN) of pyridine at 320°C and 20 bar of pressure in the absence as well as presence of parallel hydrodesulfurization (HDS) of thiophene. The effects of Ir precursor (Ir(AcAc)₃, Ir₄(CO)₁₂, H₂IrCl₆, (NH₄)₂IrCl₆), metal dispersion and sulfur addition were investigated. Ir₄(CO)₁₂ gave the most active catalyst which was ascribed to a lower amount of contaminants originated from the starting Ir compounds rather than to a better Ir dispersion. The decrease of Ir dispersion by sintering in air led to much higher decrease of the rate of C–N bond hydrogenolysis than that of pyridine hydrogenation. The Ir dispersion determined partly the HDN selectivity; a better dispersed Ir phase gave a lower amount of intermediate piperidine. Presulfidation of the reduced catalyst led to 20% decline of the rates of both consecutive HDN steps. An additional and much larger activity decline was caused by the simultaneous execution of HDS. The competitive adsorption of thiophene (or H₂S) was selectively affecting C–N bond hydrogenolysis more than pyridine hydrogenation. The alumina-supported Ir catalysts possessed much higher HDN activity and HDN/HDS selectivity than a conventional NiMo system.     

Coke study on MgO-promoted Ni/Al2O3 catalyst in combined H2O and CO2 reforming of methane for gas to liquid (GTL) process

MgO-promoted Ni/Al₂O₃ catalysts have been investigated with respect to catalytic activity and coke formation in combined steam and carbon dioxide reforming of methane (CSCRM) to develop a highly active and stable catalyst for gas to liquid (GTL) processes. Ni/Al₂O₃ catalysts were promoted through varying the MgO content by the incipient wetness method. X-ray diffraction (XRD), BET surface area, H₂-temperature programmed reduction (TPR), H₂-chemisorption and CO₂-temperature programmed desorption (TPD) were used to observe the characteristics of the prepared catalysts. The coke formation and amount in used catalysts were examined by SEM and TGA, respectively. H₂/CO ratio of 2 was achieved in CSCRM by controlling the feed H₂O/CO₂ ratio. The catalysts prepared with 20 wt.% MgO exhibit the highest catalytic performance and have high coke resistance in CSCRM. MgO promotion forms MgAl₂O₄ spinel phase, which is stable at high temperatures and effectively prevents coke formation by increasing the CO₂ adsorption due to the increase in base strength on the surface of catalyst.     

La2O3助剂对甲烷干燥重整催化剂 Ni-γ-Al2O3支撑作用的研究简

The nature of support and type of active metal affect catalytic performance. In this work, the effect of using La203 as promoter and support for Ni/γ-A1203 catalysts in dry reforming of methane was investigated. The reforming reactions were carried out at atmosphenc pressure in the temperature range of 500-2700℃. The activity and stability of the catalyst, carbon formation, and syngas （H2/CO） ratio were determined. Various techniques were applied for characterization of both fresh and used catalysts. Addition of La2O3 to the catalyst matrix improved the dispersion of Ni and adsorption of CO2, thus its activity and stability enhanced.     

Synthesis of platinum–tin/alumina reforming catalysts from a well-defined platinum–tin precursor complex

The complex [(CH₃)₄N]₃[Pt(SnCl₃)₅] was selected as a molecular precursor to prepare PtSn/γ_c-Al₂O₃ reforming catalysts. The spectroscopic fingerprints of the starting complex were obtained by ¹⁹⁵Pt and ¹¹⁹Sn NMR and diffuse reflectance UV–visible spectroscopy. A series of supported catalysts were synthesized by wet impregnation of alumina with a solution of the precursor in acetone.

Well-dispersed species are obtained for Pt loadings below 1 wt.%; at higher loadings, a second species is formed that has spectroscopic features reminiscent of the initial complex and precipitates as a separate phase. Apparently, the Pt–Sn bonds are hydrolyzed in the low-loading species and preserved in the high-loading species.

The thermal transformations of PtSn/γ_c-Al₂O₃ catalysts are also studied and compared with those of the bulk precursor. In particular, it is shown that the nature of the atmosphere of thermal treatment (neutral or oxidizing) can orient the final catalyst towards preservation of an intimate Pt–Sn interaction, or towards demixtion.     

Promotion of hydrogen permeation on metal-dispersed alumina membranes and its application to a membrane reactor for methane steam reforming

A mesoporous membrane for selective separation of hydrogen was prepared usingthe sol-gel method. Some metal salts such as RuCl₃, Pd(NH₃)₄Cl₂, RhCl₃,, and H ₂PtCl₆, were added to the boehmite sol and coated on a porous alumina substrate before firing at 500°C. It was foundthat the permeability of hydrogen and the separation factor for a hydrogen-nitrogen gaseous mixture of these metaldispersed membranes exceeded the limitations of the Knudsen diffusion mechanism. Although the gas permeation through a neat alumina membrane is governed by the Knudsen diffusion, the metals dispersed in alumina membranes were effective in promoting hydrogen permeation. These metaldispersed alumina membranes were also used in a membrane reactor for methane steam reforming at low temperature. In the temperature range of 300 to 500°C, the membrane reactor attained a methane conversion twice as high as the equilibrium value of the packed bed catalytic reactor system as a result of the selective removal of hydrogen from the reaction system.