INITIAL ACTIVITY OF REDUCED CHROMIA ALUMINA CATALYST IN N-BUTANE DEHYDROGENATION MONITORED BY ONLINE FT-IR GAS-ANALYSIS/

The initial activity of chromia/alumina catalyst (13 wt% Cr) in n-buta ne dehydrogenation was studied in a flow reactor at 853 K. The initial activity was determined by on-line FT-IR gas analysis, which enabled sampling of the gaseous product mixture at a time resolution of second s. The catalysts were processed in repeated cycles of oxidation, reduc tion, and dehydrogenation using n-butane, methane, hydrogen, or carbon monoxide as reducing agents. With n-butane, methane, and hydrogen the dehydrogenation activity was associated with Cr3+ species apparently formed in the reduction of high-valence Cr species. The catalyst reduc ed with carbon monoxide at 853 K showed poor initial selectivity for b utenes and, relative to the other catalysts, stronger formation of cok e in dehydrogenation. The initial selectivity for butenes increased wi th time on stream, however, and within 2 min reached the level obtaine d with the other catalysts. Simultaneous data relating the initial act ivity, coke content, and some of the physicochemical properties of the catalyst indicated that the surfaces of all catalysts were modified t o some extent by the successive reaction cycles. (C) 1996 Academic Pre ss, Inc.