The Morphology Control Of Several Important Industrial Zeolite Crystals And Their Catalytic Properties

Zeolites are one of the most important solid catalysts in petroleum refining and petrochemical industry. The increasing demand for petroline and consequent products require the new zeolitic mateials with high catalytic acitivity and excellent selectivity.The catalytic properties of zeolites largely depend on their morphology. And morphology of the zeolites can be controlled by changing synthesis conditions and adding various organic additives in the synthesis process. Therefore, the investigation on morphology and related catalytic performance of zeolite crytals are of great importance for practical industry.This thesis is devoted to study the morphology control and catalytic properties of three important industrial zeolite crystals (ZSM-5,, SAPO-11and SAPO-34) in the presence of organic addtives regulation. Particularly, the use of low-cost and nontoxic additives in the systhesis is very meaningful for practical industry.As an important intermediate for polymer production in industry, p-xylene is normally formed by xylene isomerization. Normally, the zeolite ZSM-5, which has a mordenite framework inverted (MFI) structure, shows superior catalytic performance for this reaction because of its shape-selectivity, ZSM-5has an anisotropic framework with two intersecting10-membered ring channels, including straight channels parallel to the b-axis and zig-zag channels parallel to the a-axis. The straight channels are favorable for mass transfer, whereas the zig-zag channels have relatively higher p-xylene selectivity. Thus, it is proposed that relatively high selectivity forp-xylene in xylene isomerization could be effectively tailored by adjusting the crystalline length along the b-axis of ZSM-5crystals. In the second chapter of this thesis, we demonstrate a rational fabrication of ZSM-5crystals with controllable b-axis length by addition of urea and starch in the starting aluminosilicate gels, a method by which sheet-like and chain-like zeolites (designated as S-ZSM-5and C-ZSM-5, respectively) are successfully synthesized. Catalytic tests in m-xylene isomerization show that p-xylene selectivity over C-ZSM-5crystals with relatively long b-axis length is improved, which is potentially important for the selective formation of p-xylene chemicals in the future.Hierarchically porous zeolites with good mass transfer and excellently catalytic properties have been attracted much attention due to the advantageous combination of both microporous zeolites and mesoporous materials. Notably, despite much encouraging progress for hierarchically porous aluminosilicate zeolites in recent years, the syntheses of hierarchically porous silicoaluminophosphate zeolites (SAPOs) are still scarce yet. Especially green method syntheses of hierarchically silicoaluminophosphate zeolites almost no reported. In the third chapter of this thesis, we report a facile synthesis of hierarchically porous SAPO-11zeolite from using low-cost and nontoxic polyhexamethylene biguanidine (PHMB) as a mesoscale template. Very importantly, after loading Pt nanoparticles Pt/H-SAPO-11catalyst exhibits higher activity, better isomer selectivity, and lower cracking product selectivity in n-dodecane hydroisomerisation than Pt nanoparticles supported on conventional SAPO-11zeolite does, which is directly attributed to the presence of hierarchical porosity in the H-SAPO-11.The superior catalytic properties of Pt/H-SAPO-11catalyst are potentially important for industrial applications of the long-chain paraffin hydroisomerization in the future.The relatively small and sole micropores in zeolites strongly influence the mass transfer in catalysis, which severely limit their catalytic performance. The problem can also be overcome by reducing the thickness of the zeolite crystal, which reduces lenghs of diffusion and consequently improving the diffusion. In the fourth chapter of this thesis, we show that a rational method synthesis of SAPO-11and SAPO-34zeolites crystal with nanosheets (20nm) morphology by using additives. SAPO-11(S-SAPO-11) nanosheets supported Pt catalyst exhibits relatively good catalytic properties in hydroisomerization of n-dodecane, compared with conventional SAPO-11, which should ascribe to the reduced crystal thickness facilities long chain isomer products diffusion and relatively suppress the further cracking of products. We expect that our synthesis approach could be applied to improve catalyst performance in long-chain paraffin hydroisomerization industry in the future.