José M. Lopes

Activity–acidity relationship in zeolite ZSM-5. Application of Brönsted-type equations

In this paper the relation between activity and acidity in a variety of ZSM-5 zeolite catalysts, with different Si/Al ratios and different protonic content, is analysed and a quantitative correlation is obtained. The acid site strength distribution was estimated using temperature-programmed desorption (TPD) of ammonia by applying a digital deconvolution method to the curves. These data were then correlated with experimental catalytic activity data for the same catalysts towards n-heptane cracking reaction, by means of a Bronsted-type equation similar to the ones used for homogeneous acid catalysis and already used for other zeolites. It can be noticed that the same types of equation that are used for homogeneous acid catalysis also hold for heterogeneous acid catalysis and that the activation energy for ammonia desorption can be used as acid-strength scale for the purpose of correlation with catalytic activity.

Ni-Ce/Zeolites for CO2 Hydrogenation to CH4: Effect of the Metal Incorporation Order

The effect of the metal incorporation order used in the preparation of bimetallic ultrastable Y (USY) zeolite catalysts for CO2 methanation has been studied. First, a Na‐USY(3) zeolite was impregnated with 5u2009% of Ni and 3u2009% of Ce in three ways: Ni before Ce (Ce/Ni), Ce before Ni (Ni/Ce), and co‐impregnation (Ni‐Ce). Stronger interactions between Ni and Ce species are established when Ni is incorporated after or simultaneously with Ce, enhancing the reducibility of the Ni species and decreasing the Ni0 average size to approximately 2.5u2005nm. However, the CO2 adsorption capacity is smaller for the sample in which Ce is incorporated before Ni. Even though larger Ni0 particles (13.3u2005nm) are formed when Ni is impregnated first, a good CO2 adsorption capacity was also observed for this sample. Co impregnation was finally found as the best preparation method, the results being confirmed for an optimized USY catalyst in terms of Ni content, Si/Al ratio, and compensating cation.