COMPARATIVE-STUDY OF CARBON-DIOXIDE REFORMING OF METHANE TO SYNTHESISGAS OVER NI LA2O3 AND CONVENTIONAL NICKEL-BASED CATALYSTS/

Carbon dioxide reforming of methane to synthesis gas was studied by em ploying a Ni/La2O3 catalyst as well as conventional nickel-based catal ysts, i.e., Ni/gamma-Al2O3, Ni/CaO/gamma-Al2O3, and Ni/CaO. It is obse rved that, in contrast to conventional nickel-based catalysts, which e xhibit continuous deactivation with time on stream, the rate of reacti on over the Ni/La2O3 catalyst increases during the initial 2-5 h and t hen tends to be essentially invariable with time on stream. X-ray phot oelectron spectroscopy (XPS) studies show that the surface carbon on s pent Ni/Al2O3 catalyst is dominated by -C-C- species that eventually b lock the entire Ni surface, leading to total loss of activity. The sur face carbon on the working Ni/La2O3 catalyst is found to consist of -C -C- species and a large amount of oxidized carbon. Both XPS and second ary ion mass spectrometry results reveal that a large fraction of surf ace Ni on the working Ni/La2O3 catalyst is not shielded by carbon depo sition. FTIR studies reveal that the enhancement of the rate of reacti on over the Ni/La2O3 catalyst during the initial 2-5 h of reaction cor relates well with increasing concentrations of La2O2CO3 and formate sp ecies on the support, suggesting that these species may participate in the surface chemistry to produce synthesis gas. It is proposed that t he interaction between nickel and lanthanum species creates a new type of synergetic sites at the Ni-La2O3 interfacial area, which offer act ive and stable performance of carbon dioxide reforming of methane to s ynthesis gas over the stated catalyst.