甲烷部分氧化Ni催化剂及助剂的研究

Ni/α-Al_2O_3 Catalyst for the Partial Oxidation of Methane to Syngas

考察了不同Ni担载量的Ni／a－Al_2O_3催化剂的催化性能，以8％Ni（质量分数）最佳．XRD分析表明，8％Ni催化剂表面NiO颗粒最小．TPR分析表明，催化剂表面主要有两种不同化学环境的NiO，当Ni担载量超过12％时，表面开始出现“游离态”NiO，这部分NiO易使催化剂积碳．添加稀土Ce有利于提高Ni催化剂的活性、选择性和稳定性，并对Ce的助剂效应作了研究．

The catalytic performance of Ni/α-Al2O3 catalysts with different nickel content wasinvestigated for the partial oxidation of methane to syngas in O2 at atmospheric pressure and veryhigh space velecity of 5×105h-1. Optimal CH4 conversion of 91%, CO and H2 selectivity of 94%and 96%, respectively were obtained over 8%(mass fraction) N1 catalyst at 800 ℃, XRD (X-rayDiffraction) analysis indicated that oxidic nickel is the main surface species on Ni/α-Al2O3 catalystcalcinated at 800℃ under atmosphere. TPR (Temperature Programmed Reduction) suggested abimodel nature of oxidic nickel that are 'fixed' to the support. The 'free' oxidie mickel, whichis responsible for the serious carbon deposition on catalyst, appearcd as the nickel content wasincreased up to 12%. Promoter effects of lanthanide oxide (CeO2) were also investigated. The results showed that addition of CeO2 was beneficial to CH4 conversion and CO selectivity. Anexcellant conversion (96.5%) and CO selection (96%) were achieved on NiCe(1%Ce)/α-Al2O3 at800 ℃ with a space velecity of 5×105h-1. Furthmore, CeO2 significantly improved the stabilityof mckel under critical reaction conditions. No carbon deposition was found over NiCe(1%Ce)/α-Al2O3 after nine hours at 900℃. The promoting mechanism of CeO2 was discussed on the basisof XPS, TPR and XRD results.