COMMUNICATIONSafter the reaction. Prior to the reaction, NiO particles were evenly dispersed on Ni/Ca,~,Sr,,TiO, (cit) and their average sizes were below 5 nm, while after the reaction they had grown to about 50 nm diameter.Ni catalysts supported on (Ca,Sr)TiO, oxidize CH, to syngas. The most active of these catalysts is Ni/Ca,,Sr,,,TiO, (cit) prepared by the citrate method from the perovskite precursor. Coke formation over Ni/Ca,,Sr,,TiO, (cit) was negligible, even after reaction for 150 h. Thus, nickel, which is abundant and cheap, can now be used in place of the expensive platinum group metals as a component of catalysts for the production of syngas.
Esper imen tal Pr ocedurrThe catalysts were prepared by the citrate, impregnation, and mixing methods. In the citrate process [lo], nickel nitrate, alkaline earth carbonates, and tetraisopropoxidotitanium were treated and heated with citric acid and ethylene glycol to make a sol This was subsequently decomposed in two steps by heating to 200'C for 5 h and then to 500 C for 5 h. and finally calcined at 850°C in air for 10 h. In the impregnation process, nickel nitrate, citric acid. and ethylene glycol were added to an aqueous suspension of the perovskite Ca,,,Sr, ,TiO,. which had previously been prepared by the citrate method. The suspension was evaporated and calcined at 850 C in air for 5 h In the mixing method. a mixture of metal oxides was ground and calcined at XSO C in air for 5 h. The Ni metal content was fixed at 8.1 wt % in all three catalysts. The Ni ;,-A1203 catalyst, used for comparison, was prepared by the impregnation method with ;,-A1,0, (Sumitomo Chemical Co., NK-124). The NI metal content uiis 11.5 wt%. The structure of the catalysts was studied by powder X-ray diffractometry (MAC Science MXP-l X diffractometer with Cu,, radiation) and X-ray photoelectron spectroscopy (PHI-5000 spectrometer employing A],, radiation and an electron flood gun). The surface areas of the catalysts (1 mzgg-') used were almost identical, as measurcd by thc N,-BET method with a Micromeritics model 2200. All the catalysts were tested at 800 C in a mixture of air (2.4 Lh-I) and CH, (1.0 L h ~ using a quartz reactor. 300 mg of catalyst was dispersed in 2 mL of quartz wool 10 avoid sintering and clogging of the reactor. Product gases were sampled immedintely after the reactor and injected into a gas chromatograph for analysis The selectivities for C , compounds, CO,. CO. and H, were calculated based on the numbers of carbon and hydrogen atoms in CH,.