STUDIES ON RUTHENIUM CATALYSTS .2. OXIDES OF THE 1ST ROW TRANSITION-ELEMENTS AS MODIFIERS OF A RU/SIO2 CATALYST

The addition of the oxides of Ca, Sc and Ti to a Ru/SiO2 catalyst increases its activity for n-butane hydrogenolysis to an extent which depends on the type of pretreatment applied; product selectivities and turnover frequencies are essentially unchanged. Adding the oxides of V, Cr and Mn, which are partially reduced under reaction conditions, leads to decreases in rate which are much more marked after high-temperature reduction (HTR; 758 K) than after low-temperature reduction (LTR; 433 K), but only modest changes in product selectivities are seen; the effectiveness in deactivation decreases with increasing atomic number. Activation energies decrease progressively with increasing modifier concentration. Numerous variables in catalyst composition, preparation and pretreatment affect the extent of interaction between modifier and metal. Failure to detect an SMSI-like effect with TiO2 is attributed to the use of a low Ti:Ru ratio (0.25). The addition of V oxide can lead to either selective or non-selective deactivation, significant changes in product selectivities occurring only in the former case. The non-selective mode was the main one in the present work.