Methane reforming With CO2 to syngas over CeO2-promoted Ni/Al2O3-ZrO2 catalysts Prepared Via a direct sol-gel process

CeO2-promoted Ni/Al2O3-ZrO2 (Ni/Al2O3-ZrO2-CeO2) catalysts were prepared by a direct sol-gel process with citric acid as gelling agent. The catalysts used for the methane reforming with CO2 was studied by infrared spectroscopy (IR), thermal gravimetric analysis (TGA), microscopic analysis, X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The catalytic performance for CO2 reforming of methane to synthesis gas was investigated in a continuous-flow micro-reactor under atmospheric pressure. TGA, IR, XRD and microscopic analysis show that the catalysts prepared by the direct sol-gel process consist of Ni particles with a nanostructure of around 5 nm and an amorphous-phase composite oxide support. There exists a chemical interaction between metallic Ni particles and supports, which makes metallic Ni well dispersed, highly active and stable. The addition of CeO2 effectively improves the dispersion and the stability of Ni particles of the prepared catalysts, and enhances the adsorption of CO2 on the surface of catalysts. The catalytic tests for methane reforming with CO2 to synthesis gas show that the Ni/Al2O3-ZrO2-CeO2 catalysts show excellent activity and stability compared with the Ni/Al2O3 catalyst. The excellent catalytic activity and stability of the Ni/Al2O3-ZrO2-CeO2 are attributed to the highly, uniformly and stably dispersed small metallic Ni particles, the high reducibility of the Ni oxides and the interaction between metallic Ni particles and the composite oxide supports.     

Partial Oxidation of Methane to Synthesis Gas over Hexaaluminates LaMAl_(11)O_(19-δ) catalysts

A series of M-substituted hexaaluminates LaMAl11O19-δ(M=Fe, Co, Ni, Mn, and Cu) were prepared and characterized by XRD, XPS, TPR and TGA techniques, respectively. They exhibited different reducibility and catalytic activity for partial oxidation of methane (POM) to synthesis gas. Among the LaMAl11O19-δsamples, LaNiAl11O19-δshowed the best catalytic activity for the topic reaction and selectivity for synthesis gas at 780℃for 2 h. The conversion of CH4 was over 99.2%, and the product selectivity for both CO and H2 was above 90.3%.     

Partial Oxidation of Methane to Synthesis Gas over Hexaaluminates LaMAl11O19-δ Catalysts

A series of M-substituted hexaaluminates LaMAl11O19-δ （M=Fe, Co, Ni, Mn, and Cu） were prepared and characterized by XRD, XPS, TPR and TGA techniques, respectively. They exhibited different reducibility and catalytic activity for partial oxidation of methane （POM） to synthesis gas. Among the LaMAl11019-δ samples, LaNiAl11O19-δ showed the best catalytic activity for the topic reaction and selectivity for synthesis gas at 780 ℃ for 2 h. The conversion of CH4 was over 99.2%, and the product selectivity for both CO and H2 was above 90.3%.     

CO_2 Reforming of CH_4 over Ni/CeO_2-ZrO_2-Al_2O_3 Prepared by Hydrothermal Synthesis Method

The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity.     

CO2 Reforming of CH4 over Ni／CeO2-ZrO2-Al203 Prepared by Hydrothermal Synthesis Method

The Ni/CeO2-ZrO2-A12O3 catalyst with different A12O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and A12O3 is stronger than that between NiO and CeO2-ZrO2. The addition of A12O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess A12O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity.     

Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al_2O_3 nanocatalyst in dry reforming of methane

MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane （DRM）. The effect of Ni loadings on the activity and coke formation of Ni/MgO-A1203 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity （GHSV） and feed ratio were studied.     

＂Intelligent＂ reforming catalysts： Trace noble metal-doped Ni/Mg（A1）O derived from hydrotalcites

Trace amounts of noble metal-doped Ni/Mg(Al)O catalysts were prepared starting from Mg-Al hydrotalcites (HTs) and tested in daily start-up and shut-down (DSS) operation of steam reforming (SR) of methane or partial oxidation (PO) of propane. Although Ni/Mg(Al)O catalysts prepared from Mg(Ni)-Al HT exhibited high and stable activity in stationary SR, PO and dry reforming of methane and propane, the Ni/Mg(Al)O catalysts were drastically deactivated due to Ni oxidation by steam as purge gas when they were applied in DSS SR ofmethane. Such deactivation was effectively suppressed by doping trace amounts of noble metal on the catalysts by using a “memory effect” of HTs. Moreover, the noble metal-doped Ni/Mg(Al)O catalysts exhibited “intelligent” catalytic behaviors, i.e., self-activation and self-regenerative activity, leading to high and sustainable activity during DSS operation. Pt was the most effective among noble metals tested. The self-activation occurred by the reduction of Ni2+ in Mg(Ni,Al)O periclase to Ni0 assisted by hydrogen spillover from Pt (or Pt-Ni alloy). The self-regenerative activity was accomplished by self-redispersion of active Ni0 particles due to a reversible reductionoxidation movement of Ni between the outside and the inside of the Mg(Al)O periclase crystal; surface Ni0 was oxidized to Ni2+ by steam and incorporated into Mg(Ni2+,Al)O periclase, whereas the Ni2+ in the periclase was reduced to Ni0 by the hydrogen spillover and appeared as the fine Ni0 particles on the catalyst surface. Further a “green” preparation of the Pt/Ni/[Mg3.5Al]O catalysts was accomplished starting from commercial Mg3.5-Al HT by calcination, followed by sequential impregnation of Ni and Pt.     

Effect of Ni Loading and Reaction Conditions on Partial Oxidation of Methane to Syngas

The partial oxidation of methane to synthesis gas is studied in this paper over Ni/Al2O3 catalysts under atmospheric pressure. The effects of Ni loading on the activity and stability of catalysts with 5 mm α-Al2O3 and θ-Al2O3 pellets as supports were measured in a continuous fixed bed reactor. It is found that the optimum Ni loading is 10%. And the effect of reaction conditions on partial oxidation of methane is also studied. The methane conversion and CO selectivity increase with the increase of the reaction temperature and the space velocity on 10%Ni/α-Al2O3 catalysts. The best CH4/O2 mole ratio is 2 for CO selectivity, and the optimum space velocity is 5.4x105 h-1.     

Syngas production by combined carbon dioxide reforming and partial oxidation of methane over Ni/α-Al_2O_3 catalysts

Ni/α-Al2O3 catalysts were found to be active in the temperature range 600 ～ 900℃ for both CO2 reforming and partial oxidation of methane.The effects of Ni loading,reaction temperature and feed gas ratio for the combination of CO2 reforming and partial oxidation of CH4 over Ni/α-Al2O3 were investigated.Catalysts of xwt%Ni/α-Al2O3(x=2.5,5,8 and 12) were prepared by wet impregnating the calcined support with a solution of nickel nitrate.XRD patterns and activity tests have verified that the 5wt%Ni/α-Al2O3 was the most active catalyst,as compared with the other prepared catalyst samples.An increase of the Ni loading to more than 5wt% led to a reduction in the Ni dispersion.In addition,by combining the endothermic carbon dioxide reforming reaction with the exothermic partial oxidation reaction,the loss of catalyst activity with time on stream was reduced with the amount of oxygen added to the feed.     

Nickel ferrite spinel as catalyst precursor in the dry reforming of methane:Synthesis,characterization and catalytic properties

Dry reforming of methane by CO2 using nickel ferrite as precursor of catalysts was investigated.Nickel ferrite crystalline particles were prepared by coprecipitation of nitrates with NaOH or ammonia followed by calcination,or by hydrothermal synthesis without calcination step.The textural and structural properties were determined by a number of analysis methods,including X-ray diffraction (XRD),Raman spectroscopy and X-ray photoelectron spectroscopy (XPS),among which X-ray diffraction (XRD) was at room and variable temperatures.All synthesized oxides showed the presence of micro or nanoparticles of NiFe2O4 inverse spinel,but Fe2O3 (hematite) was also present when ammonia was used for coprecipitation.The reducibility by hydrogen was studied by temperature-programmed reduction (TPR) and in situ XRD,which showed the influence of the preparation method.The surface area (BET),particle size (Rietveld refinement),as well as surface Ni/Fe atomic ratio (XPS) and the behavior upon reduction varied according to the synthesis method.The catalytic reactivity was investigated using isopropanol decomposition to determine the acid/base properties.The catalytic performance of methane reforming with CO2 was measured with and without the pre-treatment of catalysts under H2 in 650-800 C range.The catalytic conversions of methane and CO2 were quite low but they increased when the catalysts were pre-reduced.A significant contribution of reverse water gas shift reaction accounted for the low values of H2 /CO ratio.No coking was observed as shown by the reoxidation step performed after the catalytic reactions.The possible formation of nickel-iron alloy observed during the study of reducibility by hydrogen was invoked to account for the catalytic behavior.