PREPARATION, CHARACTERIZATION, AND ACTIVITY OF CU TIO2 CATALYSTS .2. EFFECT OF THE CATALYST MORPHOLOGY ON THE HYDROGENATION OF 1,3-CYCLOOCTADIENE AND THE CO-NO REACTION ON CU/TIO2 CATALYSTS/

The hydrogenation of 1,3-cyclooctadiene and the GO-NO reaction have be en studied on Cu/TiO2 catalysts, with reference to the effects of the preparation method and of the reductive pretreatments of the samples. In the hydrogenation of 1,3-cyclooctadiene at 433 K, a marked differen ce in activity is observed between catalysts prepared by a chemisorpti on-hydrolysis method (C) and those prepared by wet impregnation (I), t he former showing turnover numbers about 100 times greater than the la tter. This large difference in activity is ascribed to differences in the morphology of the copper species present at the surfaces of the tw o different kinds of catalysts: there are three-dimensional stepped sm all particles of Cu in the first case (C), very efficient in hydrogen dissociation, whereas there are isolated copper sites embedded in the reduced support in the second case (I), very much less active toward h ydrogen dissociation. In the GO-NO reaction, C samples show a decrease in the activity on increasing the catalyst prereduction temperature, while an opposite behavior is observed on I samples. For this reaction the rate determining step is NO dissociation; the interpretation of t he apparently conflicting data is that NO dissociation occurs efficien tly on copper sites on mildly reduced C catalysts exposing three-dimen sional copper particles and also on reduced titania sites formed in th e high-temperature reductive treatments on I catalysts. (C) 1997 Acade mic Press