费-托合成铁-钼/活性炭催化剂还原和碳化的穆斯堡尔谱研究

MOSSBAUER SPECTROSCOPIC STUDIES ON REDUCTION AND CARBURIZATION OF ACTIVATED CARBON SUPPORTED IRON -MOLYBDENUM CATALYSTS FOR FISCHER-TROPSCH SYNTHESIS

以原位穆斯堡尔谱研究了活性炭担载的费-托合成铁-钼双金属催化剂的还原和碳化行为。在H_2中不同温度下还原催化剂,其中的Fe^(3+)还原为Fe^(2+),进而还原为Fe^0。但在400—450℃间发生了还原铁物类的再氧化现象,可归因于磷钼酸根Keggin结构的热分解。在500℃H_2中,铁和钼都还原为金属并形成合金,其穆斯堡尔谱为一单峰,同质异能移为-0.16mm/s。再在300℃合成气(2H_2/CO)中碳化,可生成Fe-Mo碳化物(Fe_(1-y)Mo_y)_xC,穆斯堡尔谱为δ～0.17mm/s,△～0.64mm/s的双峰。

The reduction and carburization of activated carbon (AC) supported Fe-Mo catalysts (Fe-Mo/AC) for Fischer-Tropsch. synthesis have been studied by in situ Mossbauer spectroscopy. The catalysts were prepared by co-impregnation of AC with an aqueous solution of Fe(NO3)3 and H, [PMo12O40], and reduced in H2 at different temperatures. Fe3+ in the catalysts was easily to be reduced to Fe?via Fe2+ , but the reoxidation of the reduced iron species to Fe3+ occurred in the range of 400-450℃ owing to the thermal decomposition of the Keggin structure of phospbo-molybdate. Fe and Mo in the catalysts were reduced to metallic state at 500℃ forming Fe-Mo alloy, which showed a singlet in its Mossbauer spectra with an isomer shift of -0.16 mm/s, and the followed carburization at 300℃ in syngas (2H2/CO) converted the Fe-Mo alloy into Fe-Mo carbide, which showed a doublet with σ~0.17 mm/s and △~0.64 mm/s in Mossbauer spectra.