Selective and durable fixed‐bed catalysts are highly desirable for developing eco‐efficient HPPO(hydrogen peroxide propylene oxide)process.The powder titanosilicate catalysts must be shaped before being applied in i...Selective and durable fixed‐bed catalysts are highly desirable for developing eco‐efficient HPPO(hydrogen peroxide propylene oxide)process.The powder titanosilicate catalysts must be shaped before being applied in industrial processes.As the essential additives for preparing formed catalysts,binders are usually the catalytically inert components,but they would cover the surface and pore mouth of zeolite,thereby declining the accessibility of active sites.By recrystallizing the binder(silica)/Ti‐MWW extrudates with the assistance of dual organic structure‐directing agents,the silica binder was converted into MWW zeolite phase to form a structured binder‐free Ti‐MWW zeolite with Si‐rich shell,which enhanced the diffusion efficiency and maintained the mechanical strength.Meanwhile,due to the partial dissolution of Si in the Ti‐MWW matrix,abundant silanol nests formed and part of framework TiO4 species were transferred into open TiO_(6)ones,improving the accumulation and activation ability of H_(2)O_(2)inside the monolith.Successive piperidine treatment and fluoridation of the binder‐free Ti‐MWW further enhanced the H_(2)O_(2)activation and oxygen transfer ability of the active Ti sites,and stabilized the Ti‐OOH intermediate through hydrogen bond formed between the end H in Ti‐OOH and the adjacent Si‐F species,thus achieving a more efficient epoxidation process.Additionally,the side reaction of PO hydrolysis was inhibited because the modification effectively quenched numerous Si‐OH groups.The lifetime of the modified binder‐free Ti‐MWW catalyst was 2400 h with the H_(2)O_(2)conversion and PO selectivity both above 99.5%.展开更多
Development of highly efficient photocatalysts has emerged as a research hotspot because of their crucial role in affecting the conversion efficiency of solar energy for applications in resource exploitation and envir...Development of highly efficient photocatalysts has emerged as a research hotspot because of their crucial role in affecting the conversion efficiency of solar energy for applications in resource exploitation and environmental purification.The photocatalytic performance of the photocatalysts basically depends on the behaviors of light absorption,charge generation and separation,surface property and structural stability.Owing to its unique advantages(high surface area,tunable porosity,modifiable surface),porous silica provides an interesting platform to construct well-defined nanostructures such as core-shell,yolk-shell and other specific structures which effectively improved one or more of the above behaviors for photocatalysis.Typically,the structure with hollow morphology favors the light scattering and enlargement of surface area,while coating or binding with silica can modify the surface property of a photocatalyst to enhance the surface adsorption of reactants and physicochemical stability of catalysts.This review discusses the recent advances in the design,synthesis,formation mechanism of well-defined silica-based nanostructures,and the achievements of desired physicochemical properties for regulating the photocatalytic performance.展开更多
文摘Selective and durable fixed‐bed catalysts are highly desirable for developing eco‐efficient HPPO(hydrogen peroxide propylene oxide)process.The powder titanosilicate catalysts must be shaped before being applied in industrial processes.As the essential additives for preparing formed catalysts,binders are usually the catalytically inert components,but they would cover the surface and pore mouth of zeolite,thereby declining the accessibility of active sites.By recrystallizing the binder(silica)/Ti‐MWW extrudates with the assistance of dual organic structure‐directing agents,the silica binder was converted into MWW zeolite phase to form a structured binder‐free Ti‐MWW zeolite with Si‐rich shell,which enhanced the diffusion efficiency and maintained the mechanical strength.Meanwhile,due to the partial dissolution of Si in the Ti‐MWW matrix,abundant silanol nests formed and part of framework TiO4 species were transferred into open TiO_(6)ones,improving the accumulation and activation ability of H_(2)O_(2)inside the monolith.Successive piperidine treatment and fluoridation of the binder‐free Ti‐MWW further enhanced the H_(2)O_(2)activation and oxygen transfer ability of the active Ti sites,and stabilized the Ti‐OOH intermediate through hydrogen bond formed between the end H in Ti‐OOH and the adjacent Si‐F species,thus achieving a more efficient epoxidation process.Additionally,the side reaction of PO hydrolysis was inhibited because the modification effectively quenched numerous Si‐OH groups.The lifetime of the modified binder‐free Ti‐MWW catalyst was 2400 h with the H_(2)O_(2)conversion and PO selectivity both above 99.5%.
基金supported by the National Natural Science Foundation of China(21771070 and 21571071)the Fundamental Research Funds for the Central Universities(2018KFYYXJJ120 and 2019KFYRCPY104)。
文摘Development of highly efficient photocatalysts has emerged as a research hotspot because of their crucial role in affecting the conversion efficiency of solar energy for applications in resource exploitation and environmental purification.The photocatalytic performance of the photocatalysts basically depends on the behaviors of light absorption,charge generation and separation,surface property and structural stability.Owing to its unique advantages(high surface area,tunable porosity,modifiable surface),porous silica provides an interesting platform to construct well-defined nanostructures such as core-shell,yolk-shell and other specific structures which effectively improved one or more of the above behaviors for photocatalysis.Typically,the structure with hollow morphology favors the light scattering and enlargement of surface area,while coating or binding with silica can modify the surface property of a photocatalyst to enhance the surface adsorption of reactants and physicochemical stability of catalysts.This review discusses the recent advances in the design,synthesis,formation mechanism of well-defined silica-based nanostructures,and the achievements of desired physicochemical properties for regulating the photocatalytic performance.
