Zeolitic catalysts, post-forming

Finishing Post-Forming Manufacturing of Zeolite Catalysts and Adsorbents 71... 

The effect of silica to alumina ratios in the alkylation of aromatics is difficult to study separately because upon changing the Si/Al ratio in the thesis gel both the ratio in the zeolite and the crystal size are changed [97], as well as the crystallinity and morphology. If the Si/Al ratio is changed in a post-treatment stq> by dealumination, vsdiich can be done either by add washing or by steaming, extra framework aluminium ecies are fr>rmed. These edes can block pores and thereby modify the diffiisivities of the reactants and products in the pores and can form a complex with remaining fr-amework aluminium t diich may result in a modified addity of the catalyst. 

Zeolite beta samples with different framework and extraframework composition have been prepared by submitting the acid form of a commercial TEA-beta sample to different post-synthesis treatments, i.e. steam calcination, acid (HCl) leaching, and ammonium hexafluorosilicate (HFS) treatment. The samples were characterized by XRD, adsorption of N. at 77 K. i.r. spectroscopy with adsorbed pyridine, Si and Al MAS-NMR and XPS. Bifunctional catalysts were obtained by impregnation with 0.3 wt% Pt, and the catalytic activity for the isomerization of a simulated LSR feed (n-Cj/n-Cj, 60/40 wt%) was measured under different reaction conditions. 

The method of zeolite synthesis, the Si/Al ratio in the synthesis gel, and the crystallite size of Beta zeolite are factors to be considered for optimum alkylation performance [123,128,129[. For both USY and Beta zeolites, the amount and type of extraframework Al species (EFAL) remaining in the zeolite after calcination and/or post-synthesis treatments also affected the catalyst performance [130,131], For both zeolites, elimination of highly dispersed cationic-type EFAL formed under mild (hydro)thermal treatments decreased the alkylation... 

A linear polycyclic compound, 4,4 -dimethylbiphenyl (4,4 -DMBP), is an intermediate for making monomer of some advanced polymer materials, but the selective synthesis of 4,4 -DMBP is difficult. In this work, modifications were made on a ZSM-5 zeolite for selective methylation of 4-methybiphenyl (4-MBP) to form 4,4 -DMBP. The use of binder, deposition of basic oxide such as calcium oxide over zeolite internal and external surface can effectively improve the product selectivity. An isomorphous substitution of ZSM-5 framework A1 with Fe by a post-synthetic treatment, coupled with modification of external and internal surface by P or Ca leads to high-performance catalyst with stable activity and superior selectivity for synthesis of 4,4 -DMBP by 4-MBP methylation. 

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