Additive effects of alkaline-earth metals and nickel on the performance of Co/γ-Al_2O_3 in methane catalytic partial oxidation

Nano-sized γ-alumina （γ-Al2O3） was first prepared by a precipitation method. Then, active component of cobalt and a series of alkaline- earth metal promoters or nickel （Ni） with different contents were loaded on the γ-Al2O3 support. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction （XRD） and thermogravimetry analysis （TGA）. The activity and selectivity of the catalysts in catalytic partial oxidation （CPO） of methane have been compared with Co/γ-Al2O3, and it is found that the catalytic activity, selectivity, and stability are enhanced by the addition of alkaline-earth metals and nickel. The optimal loadings of strontium （Sr） and Ni were 6 and 4 wt%, respectively. This finding will be helpful in designing the trimetallic Co-Ni-Sr/γ-Al2O3 catalysts with high performance in CPO of methane

Catalytic Partial Oxidation of Methane over Ni/CeO_2-ZrO_2-Al_2O_3

Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.

Novel Ni/CeO_2-Al_2O_3 composite catalysts synthesized by one-step citric acid complex and their performance in catalytic partial oxidation of methane

A series of novel Ni/CeOe-Al2O3 composite catalysts were synthesized by one-step citric acid complex method, The as-synthesized catalysts were characterized by N2 physical adsorption/desorption, X-ray diffraction （XRD）, Fourier transform infrared （FT-IR） spectroscopy, hydrogen temperature-programmed reduction （Hz-TPR）, X-ray photoelectron spectroscopy （XPS） and thermogravimetry analysis （TGA）. The effects of nickel content, calcination and reaction temperatures, gas hourly space velocity （GHSV） and inert gas dilution of N2 on their performance of catalytic partial oxidation of methane （CPOM） were investigated. Catalytic activity test results show that the highest methane conversion （〉85%）, the best selectivities to carbon monoxide （〉87%） and to hydrogen （〉95%）, the excellent stability and perfect Hz/CO ratio （2.0） can be obtained over Ni/CeO2-Al2O3 with 8 wt% Ni content calcined at 700 ℃ under the reaction condition of 750 ℃, CH4/O2 ratio of 2 ： 1 and gas hourly space velocity of 12000 mL.h-1 .g-1. Characterization results show that the good catalytic performance of this composite catalyst can be contributed to its large specific surface area （~108 m2.g-1）, small crystallite size, easy reducibility and low coking rate.

Modeling of microreactor for syngas production by catalytic partial oxidation of methane

Fixed-bed reactors for the catalytic partial oxidation of methane （CPOM） to produce synthesis gas still pose hot spots problems.Microreactor is a good alternative reactor proposed to resolve these problems.In this paper,synthesis gas （hydrogen and carbon monoxide） production was investigated by a two-dimensional numerical model of single microchannel.Computational fluid dynamic （CFD） modeling with detailed chemistry was conducted to understand the CPOM on platinum （Pt） catalyst.Gas inlet velocity,microchannel pressure,and fuel to air ratio （F/A） are selected as the effective parameters on microchannel performance.Study results show that Reynolds number has considerable effect on methane conversion,hydrogen to carbon monoxide ratio （H2/CO）,and product distribution.Increasing gas inlet velocity causes all the above parameters to decrease.It is noted that increasing microchannel pressure and decreasing the ratio of fuel to air cause the decrease of the H2/CO ratio.

Structure-activity relationship in Pd/CeO2 methane oxidation catalysts

Palladium based catalysts are the most active for methane oxidation. The tuning of their composition, structure and morphology at macro and nanoscale can alter significantly their catalytic behavior and robustness with a strong impact on their overall performances. Among the several combinations of supports and promoters that have been utilized, Pd/CeO2 has attracted a great attention due to its activity and durability coupled with the unusually high degree of interaction between Pd/Pd O and the support. This allows the creation of specific structural arrangements which profoundly impact on methane activation characteristics. Here we want to review the latest findings in this area, and particularly to envisage how the control(when possible) of Pd-CeO2 interaction at nanoscale can help in designing more robust methane oxidation catalysts.

Complete Oxidation of Methane over Palladium Supported on Alumina Modified with Calcium,Lanthanum,and Cerium Ions

The activity and thermal stability of Pd/Al2O3 and Pd/（Al2O3＋MOx） （M=Ca, La, Ce） palladium catalysts in the reaction of complete oxidation of methane are presented in this study. The catalyst supports were prepared by sol-gel method and they were dried either conventionally or with supercritical carbon dioxide. Then they were impregnated with palladium nitrate solution. The catalysts with unmodified alumina had a high surface area. The activity and thermal stability of the aluminasupported catalyst was also very high. The introduction of calcium, lanthanum, or cerium oxide into alumina support caused a decrease of the surface area in the way dependent on the support precursor drying method. These modifiers decreased the activity of palladium catalysts, and they required higher temperatures for the complete oxidation of methane than unmodified Pd/Al2O3. The improvement of the palladium activity by lanthanum and cerium support modifier was observed only at low temperatures of the reaction.

Partial oxidation of methane over SiO2 supported Ni and NiCe catalysts

Nickel and nickel-ceria catalysts supported on high surface area silica, with 6 wt% Ni and 20 wt% CeO2 were prepared by microwave assisted(co) precipitation method. The catalysts were investigated by XRD,TPR and XPS analyses and they were tested in partial oxidation of methane(CPO). The catalytic reaction was carried out at atmospheric pressure in a temperature range of 400–800℃ with a feed gas mixture containing methane and oxygen in a molecular ratio CH4/O2=2. The Ni catalyst exhibited 60% methane conversion with 60% selectivity to CO already at 500℃. On the contrary, the Ni–Ce catalyst was inert to CPO up to 700℃. Moreover, the former catalyst reproduced its activity at the descending temperatures maintaining a good stability at 600℃, over a reaction time of 80 h, whereas the latter one completely deactivated. Test of CH4 temperature programmed surface reaction(CH4-TPSR) revealed a higher methane activation temperature(> 100℃) for the Ni–Ce catalyst as compared to the Ni one. Noticeable improvement of the ceria containing catalyst occurred when the reaction test started at a temperature higher than the methane decomposition temperature. In this case, the sample achieved the same catalytic behavior of the Ni catalyst. As confirmed by XPS analyses, the distinct electronic state of the supported nickel was responsible for the differences in catalytic behavior.

Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Two series of Cu/ZSM-5 catalysts, loading from 5 to 20 wt% CuO, were prepared by the deposition-precipitation and impregnation methods, respectively. The catalysts prepared by the impreg- nation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion. 20Cu（I）/ZSM-5 had the highest activity with T90% of 746 K, and for 20Cu（D）/ZSM-5, T90% was as high as 804 K. The characterization of X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, temperature-programmed desorption （TPD）, and X-ray photoelectron spectroscopy （XPS） revealed that the dispersion of copper species could be improved by using the deposition-precipitation method instead of the impregnation method, but the fraction of surface CuO, corresponding to active sites for methane oxidation, was larger on 20Cu（I）/ZSM-5 than 20Cu（D）/ZSM-5. The results of Pyridine-Fourier transform infrared spectrum （Py-FT-IR） showed that a majority of Lewis acidity and a minority of Brфnsted acidity were present on Cu/ZSM-5 catalysts. 20Cu（I）/ZSM-5 presented more Lewis acid sites. The number of Lewis acid sites changed significantly with preadsorption of oxygen. Adsorption of methane and oxygen on acid sites was observed. The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.

Partial oxidation of methane to syngas catalyzed by a nickel nanowire catalyst

A nickel nanowire catalyst was prepared by a hard template method, and characterized by transmission electron microscopy （TEM）, N2 physical adsorption, X-ray photoelectron spectrometry （XPS）, X-ray diffraction （XRD） and H2 temperature-programmed reduction （H2-TPR）. The catalytic properties of the nanowire catalyst in the partial oxidation of methane to syngas were compared with a metallic Ni catalyst which was prepared with nickel sponge. The characterization results showed that the nickel nanowire catalyst had high specific surface area and there was more NiO phase in the nickel nanowire catalyst than in the metallic Ni catalyst. The reaction results showed that the nickel nanowire catalyst had high CH4 conversion and selectivities for H2 and CO under low space velocity.

Yttria promoted metallic nickel catalysts for the partial oxidation of methane to synthesis gas

A metallic Ni catalyst was prepared with nickel sponge, followed by acid treatment. It was further promoted with yttria by an impregnation method. The catalysts were characterized by SEM, BET, XRD, TPR, XPS, etc., and studied in the partial oxidation of methane to syngas. The characterization results showed that the yttria promoted metallic Ni catalysts had high specific surface area and more NiO. The reaction results showed that the yttria promoter increased the CH4 conversion and the selectivity for H2 and CO.

Physico-Chemical Studies of Platinum-Ruthenium Catalysts of Oxidative Conversion of Methane to Synthesis-Gas

The results of studying the interaction of H2 and O2 with Pt-, Ru- and Pt-Ru catalysts supported on 2% Ce/（θ＋α）-AlEO3, at varying the ratios and concentrations of supported elements by using the temperature-programmed desorption method are presented. It has been shown that HE is adsorbed as four forms, differing in the structure, temperature, order and activation energy of desorption： HEads, HE＋ads, Hads, Hat （Tdes 〉 873 K）. The relationship of activity and selectivity of Pt-Ru catalysts with the presence of active centers able to adsorb atomic hydrogen with desorption energy （Edes） = 60-70 kJ/mol in the catalytic oxidation of methane was determined. It was found that the O2 adsorbed as two forms differing in the structure, temperature and activation energy of desorption. It has been determined that changing the atomic ratio of elements in the catalysts significantly affect on the adsorption Of OE. The introduction of ruthenium into the platinum catalyst increases the oxygen adsorption; and the surface is stabilized in a homogeneous state. Quantum chemical calculations of the activation of C-H bonds in a molecule of methane on Ru,,Pt, （m ＋ n = 4） clusters have been carried out.

Pseudo core-shell LaCoO3@MgO perovskite oxides for high performance methane catalytic oxidation

Magnesia modified LaCoO3 was prepared by a facile one-step sol-gel method and used for removal of dilute methane.Compared with the conventional doping technique,the obtained LaCoO3@MgO-x exhibits pseudo core-shell structure and shows superior catalytic activity.The methane conversion exceeds90%at 532℃on LaCoO3@MgO-0.1,while only 60%of methane is conversed using the doped perovskite LaCo0.9Mg0.1O3.The high catalytic performance of LaCoO3@MgO-0.1 is mainly attributed to the adjustment of surface acid-base properties by the MgO shell structure.According to density functional theory(DFT)calculation,the methane is more likely to be adsorbed and cracked on LaCoO3@MgO-0.1.The in situ DRIFTS shows that CH3-O-CH3 intermediate specie is formed.The pseudo core-shell structure also enhances the stability and the LaCoO3@MgO-0.1 maintains high activity after working for 100 h.The above results demonstrate that surface modification by magnesia is an effective strategy for improving LaCoO3 catalytic performance.

Nanostructured perovskite oxides as promising substitutes of noble metals catalysts for catalytic combustion of methane

Heterogeneous catalytic combustion provides a feasible technique for high efficient methane utilization.Perovskites ABO_3-type materials have received renewed attention as a potential alternative for noble metals supported catalysts in catalytic methane combustion due to excellent hydrothermal stability and sulfur resistance. Recently, the emergence of nanostructured perovskite oxides（such as threedimensional ordered nanostructure, nano-array structure） with outstanding catalytic activity has further driven methane catalytic combustion research into spotlight. In this review, we summarize the recent development of nanostructured perovskite oxide catalysts for methane combustion, and shed some light on the rational design of high efficient nanostructured perovskite catalysts via lattice oxygen activation,lattice oxygen mobility and materials morphology engineering. The emergent issues needed to be addressed on perovskite catalysts were also proposed.