Selective modification of surface and bulk V5+/V4+ ratios and its effects on the catalytic performance of Mo-V-Te-O catalysts

Abstract Selective modification of surface and bulk V 5+ /V 4+ ratios in Mo V Te O catalysts has been achieved using nitric acid and saturated ammonia solutions as pH adjustors. The addition of nitric acid strongly suppressed V 4+ in the bulk but encouraged it on the surface. Because the bulk-phase compositions of Mo V Te O catalysts varied only slightly, the changes in the catalytic performance for selective propane oxidation to acrolein resulted mainly from the variation of the bulk and surface V 5+ /V 4+ ratios. The high concentration of surface V 5+ that was responsible for propane activation led to high selectivity of propylene and high conversion of propane. Increased bulk V 4+ might result in oxygen vacancies, which promote the electron and oxygen transfer so as to increase the selectivity of deep oxidation products (CO x ). A low bulk V 4+ concentration prefers selective oxidation products; the yield of acrolein was as high as 21.4%.