研究了甲醇制丙烯(MTP)催化剂经过多周期反应后失活的本质原因,据此提出了一种简便易行的催化剂再生方法,即二次晶化法,并将其应用到失活MTP催化剂的再生中。采用X射线衍射(XRD)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N_2吸附、^...研究了甲醇制丙烯(MTP)催化剂经过多周期反应后失活的本质原因,据此提出了一种简便易行的催化剂再生方法,即二次晶化法,并将其应用到失活MTP催化剂的再生中。采用X射线衍射(XRD)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N_2吸附、^(27)Al魔角旋转固体核磁共振(^(27)Al MAS NMR)、NH_3程序升温脱附(NH_3-TPD)、吡啶吸附红外(Py-IR)光谱等测试技术对再生前后HZSM-5分子筛催化剂的晶体结构、硅铝比、织构性质、酸性质等进行了表征。并在常压(甲醇分压为30 k Pa)、反应温度为470°C、甲醇质量空速(WHSV)为1 h^(-1)的条件下,研究了再生前后HZSM-5分子筛催化剂的催化性能。结果表明,分子筛晶体结构被破坏、活性位流失是多周期反应后HZSM-5分子筛催化剂活性下降的主要原因。经过二次晶化再生后,催化剂的相对结晶度、比表面积、孔容和酸量都明显提高,晶体结构和活性位得到了有效修复,再生催化剂在MTP反应中重新表现出优异的甲醇转化能力和丙烯选择性。展开更多
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
The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting sam...The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting samples were characterized by a complementary combination of X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, X-ray fluorescence spectroscopy, XPS, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, BET and temperature-programmed desorption techniques. The results showed that the secondary crystallization of the HZSM-5 zeolite could result in migration of non-framework species from the internal channels to the zeolite surface and their transformation into framework species. The catalytic activity of these modified samples for thiophene alkylation was evaluated. Both the activity and stability of the catalysts were improved after secondary crystallization.展开更多
文摘研究了甲醇制丙烯(MTP)催化剂经过多周期反应后失活的本质原因,据此提出了一种简便易行的催化剂再生方法,即二次晶化法,并将其应用到失活MTP催化剂的再生中。采用X射线衍射(XRD)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N_2吸附、^(27)Al魔角旋转固体核磁共振(^(27)Al MAS NMR)、NH_3程序升温脱附(NH_3-TPD)、吡啶吸附红外(Py-IR)光谱等测试技术对再生前后HZSM-5分子筛催化剂的晶体结构、硅铝比、织构性质、酸性质等进行了表征。并在常压(甲醇分压为30 k Pa)、反应温度为470°C、甲醇质量空速(WHSV)为1 h^(-1)的条件下,研究了再生前后HZSM-5分子筛催化剂的催化性能。结果表明,分子筛晶体结构被破坏、活性位流失是多周期反应后HZSM-5分子筛催化剂活性下降的主要原因。经过二次晶化再生后,催化剂的相对结晶度、比表面积、孔容和酸量都明显提高,晶体结构和活性位得到了有效修复,再生催化剂在MTP反应中重新表现出优异的甲醇转化能力和丙烯选择性。
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the financial support by the Natural Science Foundation of Liaoning Province of China (Grant No.201202126)the National Natural Science Foundation of China (Grant Nos. 21276253 and 21401093)
文摘The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting samples were characterized by a complementary combination of X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, X-ray fluorescence spectroscopy, XPS, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, BET and temperature-programmed desorption techniques. The results showed that the secondary crystallization of the HZSM-5 zeolite could result in migration of non-framework species from the internal channels to the zeolite surface and their transformation into framework species. The catalytic activity of these modified samples for thiophene alkylation was evaluated. Both the activity and stability of the catalysts were improved after secondary crystallization.
