Nanosheet MFI Zeolites for Gas Phase Glycerol Dehydration to Acrolein

Abstract

To overcome the rapid deactivation of conventional ZSM-5, novel nanosheet MFI zeolites, with different Si/Al molar ratios were well fabricated. It was found that Si/Al molar ratios, do not just affect acid properties, but also determine the morphologies of nanosheet MFI zeolites by changing a-c plane areas of zeolite nanosheets. In reaction of gas phase glycerol dehydration to acrolein, the nanosheet MFI zeolites were much more active and stable than conventional ZSM-5 catalysts, owing to their suitable acidity and unique nanosheet structure. For nanosheet MFI zeolite, with Si/Al = 50 (NMZ-50), the conversion of glycerol is higher than 99% in the initial 12 h, with an acrolein selectivity of 86.6%, better than most previous reports. This superior stability of NMZ-50 can be ascribed to its low coke deposition rate and improved coke tolerance capacity. Additionally, it is interesting to find that Al contents do not just simply affect acid properties, but also determine morphologies of nanosheet MFI zeolites, and thus influence catalytic performance.

Highly Active and Selective Nano H-ZSM-5 Catalyst with Short Channels along b-Axis for Glycerol Dehydration to Acrolein

“…Here, the catalytic comparison was made based on the conversion and selectivity in the first 2 h using the best-reported catalyst. As shown in Figure , the catalyst H-ZSM-5(75) with short b -axis channels in this work has higher conversion and selectivity at a relatively high WHSV of 4 h –1 than most other catalysts. ,,,− ,,,,, The glycerol conversion and acrolein selectivity over H-ZSM-5 with short b -axis channels were similar to those over the ZSM-5 catalysts reported by Zhang et al, Huang et al, and Shan et al, although a higher WHSV was used in this work. In addition, the H-ZSM-5 with short b -axis channels exhibited a lower deactivation rate due to the medium acidity and rapid diffusion inside the catalyst.…”

“…Also, it was noticed that the catalyst reported by Huang et al deactivated much faster after the regeneration, which might be caused by the reduced “zeolitic behavior” of hierarchical zeolites in terms of hydrothermal stability. A good catalytic performance was obtained with the nanosheet MFI zeolite reported by Shan et al, but the synthesis method was much more complex. Specifically, the template [C 18 H 37 -N + (CH 3 ) 2 -(CH 2 ) 6 -C 6 H 13 )]­Br 2 used in this method was critical but difficult to synthesize.…”

Cooperation of hierarchical pores with strong Brønsted acid sites on SAPO-34 catalysts for the glycerol dehydration to acrolein

“…11C, the highest acrolein yield of 89.8% can be achieved over the A(0.01M) at a WHSV of 3.7 h -1 . Compared with the best results in previous literatures (Cg = 100%, Yacro = 80.6% on the hierarchical SAPO-40 under a WHSV of 0.85 h -1 ; Cg = 100%, Yacro = 72% on the modified ZSM-5 under a WHSV of 0.75 h −1 ; Cg = 99%, Yacro = 86.6% on the nanosheet ZSM-5 under a WHSV of 2.1 h -1 ) [15,64,66,68], the A(0.01M) catalyst in our work exhibits the best catalytic performance (Cg = 100%, Yacro = 89.8% on the hierarchical SAPO-34 with strong Brønsted acid sites under a WHSV of 3.7 h -1 ) for the production of acrolein from glycerol among the zeolite samples under similar reaction conditions so far.…”

Progress of the Catalytic Deactivation of H‐ZSM‐5 Zeolite in Glycerol Dehydration

“…In contrast, the MCM-22 zeolite reached a conversion lower than 20 %, once zeolite micropores were inaccessible to glycerol. Besides, as Shan et al [84] discussed, the crystal and particle size of the catalysts also influences the coking since zeolites with smaller crystals have shorter channels, minimizing the coking rate. [84,85] The authors, [84] using nanosheets of H-ZSM-5 zeolites with Si/Al ratio of 100, obtained 92 % of glycerol conversion and 86 % of acrolein selectivity even for 8 h of reaction due to the low coke deposition.…”