Asima Sultana

A comparative and multitechnical approach to the acid character of templated and non-templated ZSM-5 zeolites

Abstract ZSM-5 zeolites with varying SiO 2 /Al 2 O 3 ratios (28, 50, 75, 100, 150) were synthesized with and without the aid of a template. The molar oxide compositions of the reactants were x SiO 2 :Al 2 O 3 : y Na 2 O:1500 H 2 O with x =28–150 and y =6.7. The samples were characterized by XRD, IR, SEM, and BET surface area measurements. The zeolites synthesized with template were found to be pure. Non-templated zeolites with SiO 2 /Al 2 O 3 greater than 50, however, contained α-quartz along with ZSM-5. The acidity was measured by stepwise temperature-programmed desorption (STPD) of ammonia and calorimetric heats of adsorption of ammonia. The number of acid sites decreased almost linearly with the SiO 2 /Al 2 O 3 ratio of the zeolites. It was found that the acidity of zeolites measured both by STPD of ammonia and calorimetry was in fairly good agreement. Aniline alkylation and cumene cracking reactions were carried out over the two series of zeolites to evaluate the catalytic properties involving acidity. Cumene-cracking was correlated with the number of strong acid sites in the zeolite as determined by microcalorimetry. In both series of zeolites, certainly Bronsted and Lewis acid sites were present. The possible presence of more Lewis sites in non-templated zeolites than in templated zeolites might be responsible for high aniline alkylation and low cumene-cracking activity.

Effect of SiO2 support properties on the performance of Cu–SiO2 catalysts for the hydrogenation of levulinic acid to gamma valerolactone using formic acid as a hydrogen source

Vapor phase catalytic transfer hydrogenation of aqueous levulinic acid (LA) with formic acid (FA) as a hydrogen source was carried out over copper loaded on to several SiO2 supports having different physicochemical properties. The SiO2 supports and Cu–SiO2 catalysts with different support properties were characterized by XRD, TPR, XPS, NH3-TPD and UV-vis techniques to evaluate the copper species and its interaction with the support. The SiO2 support alone showed lower LA conversion and low selectivity to GVL whereas Cu–SiO2 catalysts were found to show high conversion and selectivity to the desired product with formic acid as the hydrogen source. The difference in the activities and product selectivity among different copper supported silica appears to be a complex function of acidity and the nature of copper species in the Cu–SiO2 catalysts. No direct correlation was observed between a specific catalyst property such as acidity and pore size, and the performance of the Cu–SiO2 catalysts. From the characterization, it appears that the species responsible for higher activity and selectivity to GVL are monomeric partially oxidized copper species in a strong interaction with the support in combination with a higher number of acid sites, both of which are present in Cu–SiO2-Q6. Cu–SiO2-Q6 showed the highest conversion and selectivity of 66 and 81%, respectively, under optimized conditions.

Effect of Acid–Base Properties on the Catalytic Activity of Pt/Al2O3 Based Catalysts for Diesel NO Oxidation

The activity of Pt catalysts supported on Al2O3 modified with various acid–base additives has been investigated for oxidation of NO to NO2. Although Pt dispersion was changed by the additives, there was no clear effect of Pt dispersion on the catalytic activity. The measurement of solid acid–base properties of the modified Pt/Al2O3 indicated that the NO oxidation activity increased by the increase of surface density of strong acid sites and decreased by the increase of basic sites. It was suggested that platinum on the acidic supports keeps its highly active metallic state for NO oxidation, while the formation of nitrate/nitrite on the basic supports inhibits the reaction on the Pt surface.

Enhanced NOx Conversion with Decane Over Ag/Al2O3 and Metal Supported ZSM-5 Composite SCR Catalysts

A combination of Ag/Al2O3 and a partial oxidation catalyst M/ZSM-5, M being different metal cations, were evaluated for selective catalytic reduction of NO with decane. Physical mixture of Ag/Al2O3 and M/ZSM-5 catalysts showed significant increase in NOx conversion compared to single component Ag/Al2O3 catalyst. M/ZSM-5 as a second catalyst component was found to generate more reactive hydrocarbons, such as unsaturated small chain hydrocarbons and oxygenates in situ, and enhance the NOx conversion over Ag/Al2O3 HC-SCR catalyst.