Fluoride and sulfate treatment of AlPO4-Al2O3 catalysts. I: Structure, texture, surface acidity, and catalytic performance in cyclohexene conversion and cumene cracking

Abstract Anion-treated (APAl-P-F) and APAl-P-S) catalysts contain both tetrahedral and octahedral Al (their ratio varies with anion type), while P always remains in P(OAl) 4 environments. Moreover, two types of Al surface OH groups at 3786 and 3738 cm −1 and only one type of P surface OH group at 3670 cm −1 are found in the DRIFT spectra of the APAJ-P catalyst. All OH types are reduced by anion treatment, especially in the case of the F − ion (APAl-P-F). However, all catalysts retain some hydroxyl groups after anion treatment. The presence of F − or SO 2− 4 ions increases both the number and strength of acid sites and so all anion-modified APAI-P catalysts exhibited increased catalytic activity with respect to the unmodified ones in cyclohexene and cumene transformations. Also, each reaction responded in a similar way to anion modification. Moreover, APAl-P-F catalysts have increased activity as compared to the sulfated ones in both reaction processes. The maximum catalytic activity of APAl-P-F catalysts was observed when the fluoride loading was 2.5 wt%. In cyclohexene conversion, the anion type also causes a change in the reaction process. Thus, pure APAl-P and APAl-P-S catalysts are selective for cyclohexene isomerization while APAl-P-F catalysts exhibit both isomerization and hydrogen transfer activities, the former always being predominant. Maximum selectivity towards cyclohexene isomerization products is obtained at lower conversion, while the selectivity towards hydrogen transfer products (methylcyclopentane plus cyclohexane) increases with the fluoride content and reaction temperature.