EFFECT OF COBALT SOURCE ON THE REDUCTION PROPERTIES OF SILICA-SUPPORTED COBALT CATALYSTS

被引:129
作者
ROSYNEK, MP
POLANSKY, CA
机构
来源
APPLIED CATALYSIS | 1991年 / 73卷 / 01期
关键词
CATALYST CHARACTERIZATION (TPD; XPS; XRD); COBALT; OXIDATION STATE; REDUCTION; SILICA SUPPORTS; CARBON MONOXIDE HYDROGENATION;
D O I
10.1016/0166-9834(91)85115-C
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The bulk and surface reduction properties of silica-supported cobalt catalysts are influenced by the identity of the cobalt salt employed in catalyst preparation. Temperature-programmed reduction (TPR), X-ray powder diffraction (XRPD), and X-ray photoelectron spectroscopy (XPS) have been used to characterize the reduction, calcination, and catalytic behaviors of a series of 6 wt.% Co/SiO2 catalysts prepared from nitrate, chloride, and acetate precursors. TPR profiles in hydrogen of the uncalcined catalysts reveal that reduction of Co(NO3)2/SiO2 occurs via an initial reductive decomposition of the nitrate ions, producing CoO(x)-SiO2 surface species that are much more difficult to reduce to metallic cobalt than is the unsupported nitrate salt. Complete reduction of the silica-supported acetate is also markedly inhibited compared to that of the unsupported salt. By contrast, reduction of CoCl2/SiO2 occurs in a single step that is virtually unaffected by the presence of the silica support. XRPD analysis confirms that precalcination of the three catalysts at 500-degrees-C prior to reduction leads to the formation of Co3O4 with the nitrate- and chloride-derived catalysts, but not with the acetate-derived material. TPR profiles and XPS spectra indicate that isothermal reduction in hydrogen at 400-degrees-C is much less complete for the uncalcined catalysts than for the calcined materials, particularly for the nitrate and acetate precursors. Exposure of the uncalcined, hydrogen treated catalysts to a H-2/CO reaction mixture at 250-degrees-C results in further reduction of Co2+ to Co0 for the nitrate- and acetate-derived catalysts, which had been only slightly reduced by the prior hydrogen treatment, and partial re-oxidation of Co0 to Co2+ for the chloride-derived material, which had been largely reduced by the hydrogen treatment.
引用
收藏
页码:97 / 112
页数:16
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