This work has firstly constructed purely Lewis acidic sites on MCM-41 successfully, for which Zr-MCM-41 catalysts with different Zr contents are prepared through the hydrolysis of ZrOCl 2 on MCM-41, followed by calcination . Thus-prepared materials possess typical hexagonal mesostructures, irregular morphologies, large surface areas, and large pore sizes, as revealed by XRD , SEM, TEM, N 2 adsorption, and DRIFT FTIR. UV–vis, Raman and XPS spectra prove the formation of isolated species in high dispersion on the surface of MCM-41. NH 3 -TPD analysis shows that the acid intensity of the catalysts is proportional to the content of Zr, and the acidity of Zr-MCM-41 with the Zr content of <0.5% is very weak. Pyridine-IR spectra show that the surface acidity is mainly consisted of Lewis acidity, and solely Lewis acidic sites are constructed on Zr-MCM-41(550) with a low Zr content < 0.5 wt%. More Lewis acidic sites exposed on the surface of Zr-MCM-41 are considerably important for promoting the titled Prins condensation.
Lincai Peng,Xueying Gao,Xin Yu,Hui Li,Junhua Zhang,Liang He
An integrated multistep catalytic process in a one-pot cascade model to realize conversion is preferred in terms of process economics and energy efficiency. Here, we present the noble-metal-free but highly effective catalytic transfer hydrogenation and acid-catalyzed conversion of biomass-derived furfural for direct production of biofuel alkyl levulinate using alcohols as the hydrogen donor and reaction medium. With optimization of the process variables, a high yield of alkyl levulinate at up to 85.3% could be captured under mild conditions in isopropanol medium with the combination of Zr-MCM-41 and Amberlyst-15 catalysts. The reaction proceeds via the catalytic transfer hydrogenation of furfural to furfuryl alcohol over Zr-MCM-41, which is then converted to alkyl levulinate by an Amberlyst-15 acid catalyst. The spent hybrid catalysts could be effectively recovered from the resulting reaction mixture and reused 5 times with little deactivation after plain regeneration treatment.
Jisheng Xu,Chengxiang Shi,Shuguang Zhang,Qiancheng Zheng,Lun Pan,Xiangwen Zhang,Ji-Jun Zou
Comprehensive Summary Non-oxidative ethane dehydrogenation is a promising route to produce ethene. Herein, PtSn supported catalysts were investigated to achieve better ethane dehydrogenation performance by introduction of different Zr promoters, i.e. , framework Zr and ZrO 2 , to mesoporous MCM-41. In-situ XRD, TEM and CO chemisorption show that aggregation of metal particles and phase segregation of Pt 3 Sn to Pt and PtSn 3 at high temperature occur for PtSn/M, leading to bad ethane dehydrogenation activity. Strong interaction between ZrO 2 and PtSn species, as proved by XPS, results in restrained metal particles, which promotes the initial reactivity. However, Pt phase generated on surface is disadvantageous for the desorption of produced ethene as indicated by CO-IR and C 3 H 6 -TPD, and pyridine-IR and NH 3 -TPD indicate strong acidity generated. Both deactivate the catalyst rapidly by deep dehydrogenation and coking. Moderate interaction between PtSn species and Si-O-Zr with much weaker acidity is formed when framework Zr is incorporated into MCM-41, which benefits the dispersion of metal particles, formation of Pt 3 Sn/Pt species and stabilization of metal species from phase segregation. Outstanding initial ethane conversion and ethene selectivity of ca. 99% were achieved for the optimal PtSn/ZrM, which is more coking-tolerant and stable by generating graphitic carbon mainly on support instead of active metals.
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