Tailoring The Microstructure Of Alumina Support Toward Enhanced Performance Of Reforming Catalysts

Catalytic reforming is an important way to improve the research octane number(RON)of gasoline and produce a variety of chemical raw materials.The morphology,pore structure and surface properties of alumina support significantly affect the loading of active metal,reaction-diffusion and carbon deposition behavior.Therefore,it is urgent to understand the influence of alumina support microstructure on the performance of reforming catalysts,so as to guide the structural design and performance enhancement of them.To the end,the effects of pore size,porosity and the aspect ratio of rods on the catalytic performance over reforming catalysts are primarily illustrated by numerical simulation with rod-like and sphericle particles as the smallest stacking units;subsequently,the effects of synthesis conditions on the morphology and pore structure of alumina support are investigated by the hydrothermal,alkoxide hydrolysis and recrystallization method;finally,Pt-based catalysts with different microstructure alumina support are fabricated,and the structure-activity relationship is revealed by changing the microstructure of catalyst.The main findings are as follows:(1)The structure-activity relationship for microstructure(porosity,pore size,rod aspect.ratio)of catalyst and reforming performance is correlated based on the particle bed model established by COMSOL Multiphysics numerical simulation analysis.Increasing the porosity from 0.7 to 0.95 and decreasing the pore size from 16 nm to 10 nm can increase the conversion of heptane by 5.0%and 7.5%,respectively.The best aspect ratio of rods is in the range of 7 to 15.When the aspect ratio is 15,the conversion of n-heptane with rod-like catalyst is 43%higher than that of spherical one,which indicates that the effects of morphology on the conversion are more significant than pore structure.(2)The regulation of alumina morphology is elucidated by changing reaction temperature,reaction time and aging time.The growth process of controllable synthesis of alumina rods is revealed.Reaction temperature and reaction time mainly affect the axial growth of Al(OH)4-gel ligands.Aging time dominates the Ostwald ripening process of rod-like crystal surface.The integrated growth mechanism of alumina rods is proposed.The kinetic equations for the hydrothermal synthesis of alumina rods are established.(3)The synthesis of alumina with high pore volume by alkoxide hydrolysis is studied.The regulation of pseudo-boehmite pore structure is clarified by changing hydrolysis temperature,rate and time.Pseudo-boehmite with higher pore volume and specific surface area is obtained when the hydrolysis rate is faster and the hydrolysis temperature is closer to the critical crystallization temperature.Pseudo-boehmite with highest pore volume of 1.28 cm3/g can be prepared in 50℃(hydrolysis temperature),1.0 mL/min(hydrolysis rate)and 50 min(hydrolysis time).Based on the kinetics equations,the alumina rods with high pore volume are successfully synthesized.(4)The effects of alumina microstructure on catalytic reforming performance of n-heptane are revealed.Compared with the rod-like catalyst or amorphous alumina catalysts with high pore volume,the rod-like alumina catalyst with high pore volume shows higher toluene selectivity and carbon deposition resistance.The aromatization rate of five membered rings(e.g.ethyl cyclopentene)is further improved at low space velocity by using catalyst pellets.