Enhanced Stability of HZSM-5 Supported Ga2O3 Catalyst in Propane Dehydrogenation by Dealumination

Abstract

Gallium oxide catalysts supported on HZSM-5 with different Si/Al ratios were characterized by pyridine adsorption FT-IR, model reactions and XPS studies. As the Si/Al ratio of the support HZSM-5 zeolite rises, the acidity of the supported catalysts decreases accordingly, which comes from two aspects: the loss of acid sites present on HZSM-5 support and the loss of the acid sites present on gallium oxides. The latter was caused by the change in the interaction between Ga 2 O 3 and support. The initial activity in the propane dehydrogenation decreases with increasing Si/Al ratio while the stability increases. The enhanced stability is thought to be caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization.

Dehydrogenation of Propane to Propylene over Ga2O3Supported on Mesoporous HZSM‐5 in the Presence of CO2

“…The initial propane conversion decreases as the Si/Al ratio increases, due to the decrease of the acid sites on the catalysts, quite similar to the results over Ga 2 O 3 /HZSM-5 catalysts. 16 Meanwhile, the selectivity to propylene increases with the increase of Si/Al ratio. Thus, the initial propylene yield has the sequence of Figure 4B.…”

“…Similar results were observed before. 16,17 The catalytic activities of these supported gallium oxide catalysts toward cumene cracking, a typical strong acid catalyzed reaction, have been investigated. The results are given in Table 2.…”

“…This enhancement can be attributed to the reverse water gas shift reaction, which accelerates the formation of the dehydrogenation products by transforming H 2 with CO 2 into CO and H 2 O. 9,16 It can also be seen that the stability of the catalysts is improved after the addition of CO 2 . The initial activity of Ga 2 O 3 /M-HZSM-5(240) catalyst dropped about 22.4% within 30 h in the absence of CO 2 , but when CO 2 was introduced, only 16.5% was dropped within the same period.…”

“…The superb stability can be explained by the decrease in the amount of acid sites with medium to strong strength, which can suppress the side reactions such as oligomerization, cyclization, cracking and aromatization. 17 Further study shows that the stability can also be enhanced by the introduction of mesopores through steaming, due to the promotion of desorption and diffusion of the propylene. 18 Mesoporous ZSM-5 is a kind of zeolite containing both wormhole-like mesopores as well as micropores of MFI structure.…”

“…[10][11][12][13][14][15] Our recent work shows that high Si/Al ratio HZSM-5 supported Ga 2 O 3 is highly active and stable in dehydrogenation of propane to propylene in the presence of CO 2 . [16][17][18][19] The propylene yield can stabilize at about 22% in 100 h without obvious deactivation. The superb stability can be explained by the decrease in the amount of acid sites with medium to strong strength, which can suppress the side reactions such as oligomerization, cyclization, cracking and aromatization.…”