Effect of steam treatment on catalytic performance of HZSM-5 catalyst for ethanol dehydration to ethylene

The effect of steam treatment on HZSM-5 catalysts was analyzed during ethanol dehydration to ethylene. The parent and the steam treated HZSM-5 catalysts were characterized by various techniques. The results showed that the steam treatment created new mesopores on HZSM-5 zeolites by increasing the treatment temperature, which resulted in the coexistence of micropores and mesopores. The total amount of acid sites and the Brönsted/Lewis ratios of HZSM-5 zeolites decreased after steam treatment, especially for the strong acid sites. The steam treated catalyst at 500 °C (HT500) exhibited excellent catalytic stability and good selectivity for ethanol dehydration to ethylene. The improvement in the catalytic stability can be attributed to lower acidity, lower ratio of B/L and newly created mesopores after steam treatment. The analyses of the coke depositions over the spent catalysts indicated that the HT500 catalyst contained less coke deposition than that over the parent HZSM-5 did. The newly created mesopores on catalyst during the steam treatment may accommodate part of coke deposition, suppressing the formation of coke deposition in its inherent micropores to some extent.

The stability of the parent HZSM-5 and the HT500 catalyst (reaction condition: HZSM-5, T = 250 °C; HT500, T = 275 °C, WHSV = 2.37 h− 1, 20 (v) % ethanol).Figure optionsDownload as PowerPoint slideHighlights
► The steam treatment reduces both the total number of acid sites and the B/L ratio, and creates new mesopores over the HZSM-5 zeolite.
► Both the changes in the catalyst acidic properties and in the porous structure contribute to the improvement in the catalyst stability.
► The HT500 catalyst contains less coke deposition than over the parent HZSM-5 and facilitated the formation of light coke.
► The newly created mesopores during the steam treatment may accommodate part of coke deposition.