Shaping Y-Zeolites using in situ formation of alumina and AlPO binders: Coke-resistant catalysts for the cracking of methylcyclohexane

Abstract

Endothermic catalytic cracking of hydrocarbon fuels over solid acid catalysts has been considered a potential heat sink to offset the thermal loads on high-speed flight vehicles, thus maintaining their catalyst stability and activity. Which is essential as an effective heat sink and produce fuels for sustained flight. The present work demonstrates a novel approach of dispersing zeolite in a catalyst matrix containing inorganic binders such as alumina and aluminum phosphate (ALPO) to improve the thermal, mechanical stability as well as the coke-resistance of Y-zeolites during catalytic cracking of endothermic fuels. Synthesis of such binders modified zeolite was achieved by adding Y-zeolite to pseudo boehmite, an alumina precursor followed by its hydrolysis in the presence of either nitric acid or phosphoric acid, which led to the formation of Alumina or ALPO modified zeolites. During this process, partial removal of alumina from the zeolite framework functions as seed for the growth of alumina and AlPO binders which together form a catalyst matrix consisting of zeolite and binder. Three different Y-Zeolites of varying Si/Al ratios were modified with alumina and ALPO binders using the afore-mentioned process. N2 sorption isotherms, Ammonia TPD, Solid state NMR and SEM imaging showed that these two binders modified the textural, structural, and acidic sites of the zeolites. Catalytic cracking of methylcyclohexane (model endothermic fuel) over these binder modified zeolites was carried out to study their performance and determine the conversion of methylcyclohexane, catalyst stability, product selectivity and coke deposition. Alumina and AlPO binders were observed to have differential binding with the zeolite acid sites, therefore the resultant catalyst activity, product activity and coking behavior were also found to be different. The alumina modified zeolites showed a slight decrease in the catalytic activity but promoted the formation of coke which can be easily oxidized and the selectivity towards cracked products than their isomers. In contrast, AlPO modified zeolites exhibited decreased catalytic activity but also decreased the coking considerably. Spent catalysts characterization clearly demonstrated that the binder modification of zeolites improved the catalyst stability, products selectivity, coke deposition, nature of coke and the amount of coke deposition.