Improved Industrial Catalysts: Part 1, Catalysts for NO and NOx Removal: Final Report

摘要

A careful investigation with many tools has been undertaken of the reaction of NOx and ammonia over vanadia-titania catalysts in the presence of oxygen. An understanding of a novel mechanism has been achieved which indicates that the catalytic reaction is essentially a redox reaction of 5 valent and 4 valent vanadia. In an attempt to produce improved catalysts, it has been proposed to use pelleted catalysts instead of the honeycomb catalysts currently being used commercially. This would save a great deal of expense in catalyst manufacture, but requires that the pelleted catalysts be hard enough to withstand abrasion at very high gaseous space velocities. It has been found that extrusion of titania containing vanadia in the presence of some phosphoric acid as a binder gives sufficiently hard catalysts which, however, show a loss of activity of about 10%. This loss of activity has been traced to the formation of surface vanadium phosfates and titanium phosfates. Life tests have shown that while loss of activity prevails over long periods of time, the activity curve for the non-phosphorous containing and the phosphorous containing catalysts are parallel. It has also been shown that by reducing the space velocity by about a factor of 2, activities of the phosphorous containing catalysts match that of the non-phosphorous containing catalysts. This means that the catalyst volume will have to be about double, which probably still presents an advantage over the expensive honeycomb catalyst. 19 refs., 33 figs., 20 tabs.