Highly selective 1-heptene isomerization over vanadium grafted mesoporous molecular sieve catalysts

Mesoporous molecular sieve supported vanadium catalysts (V-MCM-41, V-SBA-15 and V-TUD-1) with different pore structures and pore sizes were prepared via a post-synthesis grafting method using atomic layer deposition. Nitrogen physisorption and X-ray diffraction demonstrated that ordered mesoporous structures for all samples were attained after grafting procedures. UV-vis and UV-Raman spectroscopies suggested that highly dispersed vanadium units were formed on the pore wall surface. Ammonia temperature-programmed desorption and IR spectroscopy of adsorbed pyridine suggested the existence of mild acidity, containing both Lewis and Brønsted sites; the ratios of Lewis/Brønsted acid depended on the structure of the catalyst support. The isomerization of 1-heptene was employed as a reaction probe to characterize the acid properties of these catalysts with moderate acid strengths. No methyl migration isomerization was observed since a stronger acidity was required. Conversion as high as 92% at 600. K and isomer selectivity over 90% (mainly double bond shift products) over the V-SBA-15 catalyst were achieved. The catalytic performances, including activities, selectivities, 2-heptene to 3-heptene ratios, and cis-heptene/. trans-heptene ratios, over different mesoporous supported catalysts were compared and discussed in detail. The catalyst deactivation was also explored.