No abstract

The generation of synthesis gas (hydrogen and carbon monoxide mixture) from two global warming gases of carbon dioxide and methane via dry reforming is environmentally crucial and for the chemical industry as well. Herein, magnesium-promoted NiO supported on mesoporous zirconia, 5Ni/xMg-ZrO 2 (x = 0, 3, 5, 7 wt%) were prepared by wet impregnation method and then were tested for syngas production via dry reforming of methane. The reaction temperature at 800 °C was found more catalytically active than that at 700 °C due to the endothermic feature of reaction which promotes efficient CH 4 catalytic decomposition over Ni and Ni-Zr interface as confirmed by CH 4-TSPR experiment. NiO-MgO solid solution interacted with ZrO 2 support was found crucial and the reason for high CH 4 and co 2 conversions. The highest catalyst stability of the 5Ni/3Mg-ZrO 2 catalyst was explained by the ability of CO 2 to partially oxidize the carbon deposit over the surface of the catalyst. A mole ratio of hydrogen to carbon monoxide near unity (H 2 /CO ~ 1) was obtained over 5Ni/ZrO 2 and 5Ni/5Mg-ZrO 2 , implying the important role of basic sites. Our approach opens doors for designing cheap and stable dry reforming catalysts from two potent greenhouse gases which could be of great interest for many industrial applications, including syngas production and other value-added chemicals. The production of syngas (a mixture of H 2 and CO) through dry reforming of methane is an excellent strategy to reduce the global warming effects of carbon dioxide (CO 2) and methane (CH 4). Noble metals such as palladium (Pd), platinum (Pt), and ruthenium (Ru) have been used for this purpose, but costly precursors and instability of catalyst, at high reaction temperature around 800 °C, have limited their application 1. On the other hand, costeffective nickel (Ni) metal, supported on an appropriate supports such as alumina 2 , mesoporous silicates 3-7 , and zirconia 8-10 , has been found to withstand at this reaction temperature (800 °C). In this context, many researchers have followed the surface modification methodology to optimise the catalyst performance because Ni-based catalyst is also prone to deactivation. The first series of modifications were carried out over alumina supports

Hydrogen production through methane dry reforming holds the promise of lowering greenhouse gases, that is CO2 and CH4, concentrations. Herein, Ca‐, Cr‐, Ga‐ and Gd‐promoted lanthana‐zirconia–supported Ni catalysts are investigated and characterized by X‐ray diffraction, Raman, infrared and UV‐vis spectroscopy, CH4‐temperature programmed surface reaction and cyclic reduction‐desorption experiment. All promoted catalyst systems had high and constant hydrogen yield (>70%) due to pronounced reoxidation capacity of reduced ‘NiO species strongly interacted with support’ through oxygen replenishment by CO2. The presence of mixed oxide and regeneration of reduced catalyst up to optimum level through oxygen replenishment by CO2 in Gd, as well as Cr‐promoted catalyst, outperformed (80% initially) than other promotors, Ca and Ga. In the long run (440 min to 33 h), Cr‐promoted catalyst system performed better than Gd‐promoted catalyst system as H2 yield remained constant ~79% due to the smallest energy gap between valance and conduction band, Ni‐Cr interaction species for wide range CH4 decomposition and chromate species for profound carbon deposit oxidation.

Summary Ceria promoted phosphate‐zirconia supported nickel catalyst (10Ni1Ce/PZr; x = 0, 1, 1.5, 2, 2.5, 3, 5 wt%) are prepared and characterized by XRD, SEM, SEM‐EDX, CH4‐TPSR, NH3‐TPD, cyclic H2TPR‐CO2TPD‐H2TPR, and TPH. Ceria addition induces surface reducibility, exposes reduced phases of NiO and Ni2P2O7 as CH4 decomposition sites, and persuades additional CO2 adsorbed species as formate species over the catalyst surface. It also switches mobile oxygen in the lattice and thereafter oxide vacancy is replenished by oxygen from CO2 to a great extent. Altogether, 1 wt% ceria loading (10Ni1Ce/PZr) ensures more than 90% H2 yield (H2/CO = 0.96) whereas 2 wt% ceria loading inputs constancy in catalytic performance up to 440 min TOS. Up to 3 wt% ceria loading, 97% hydrogen yield (H2/CO ~1) is observed. Catalytic performance deteriorated above that 3 wt% ceria loading due to shading the catalytic active site or reoxidation of metallic nickel by excess ceria.