Ring Enlargement of Methylcyclopentane over Pt/(HZSM-48+pseudoboehmite) Catalysts

Abstract

Platinum catalysts loaded on a hybrid support, composed of HZSM-48 and pseudoboehmite, were applied to the synthesis of benzene through methylcyclopentane (MCP) reforming in order to investigate the effect of the addition of pseudoboehmite to Pt/HZSM-48 for ring-enlargement reaction. A total of 0.5 wt% of platinum was impregnated on the hybrid support by using the incipient wetness method. Catalyst characterization was performed with nitrogen sorption, X-ray diffraction, temperature-programmed desorption of NH3, and infrared spectroscopy of adsorbed pyridine. It was found that mesoporous structures were well-developed in Pt/(HZSM-48 + pseudoboehmite) catalyst as a result of the pseudoboehmite addition, of which the average pore size was in the range of 7–8 nm. The presence of pseudoboehmite in the catalyst increases the total amount of acid sites and weakens the acid strength, compared with those of the Pt/HZSM-48 catalyst. Lewis acid sites were more abundant than Brönsted acid sites over the Pt/(HZSM-48+pseudoboehmite) catalysts. It was found that selectivity to the ring-enlargement reaction is dominant over selectivity to the ring-opening reaction over the Pt/(HZSM-48 + pseudoboehmite) catalysts. The benzene yield over Pt/(HZSM-48 + pseudoboehmite, 1:1) catalyst reached 65.1% at 450 °C and 0.3 h−1. As well as being influenced by the mesoporous structure, the higher activity and selectivity in MCP reforming was also determined by appropriate acidity of the Pt/(HZSM-48 + pseudoboehmite) catalysts.

Synthesis of pseudoboehmite – effect of acetate ion

“…The precipitations were performed at room temperature, adopting after the synthesis, for all samples, the aging time of 96 h, at the boiling temperature. For the synthesis of pseudoboehmites, 8 trials were obtained, organized in a factorial experimental design of 2 3 , in which the variables are the reagents themselves, classified as Aluminum Salt (A), Acetate (B) and hydroxide (C), all divided into (+1) and lower levels (-1), in order to analyze its effects on the properties of obtained product. In the factorial experimental design, the error can be estimated using the interactions of 3 orders.…”

“…The results listed in Table 3 were treated using the 2 3 factorial experimental design and the results are presented in Table 4.…”

“…According to the data and taking the calculations for factorial planning 2 3 we determined the corresponding specific surface area results which are listed in Table 6. Note that the variables A and C, individually, are not significant in relation to the specific area, but again the interactions are significant for the specific surface area results.…”

“…The presence of pseudoboehmite in the catalyst Pt/(HZSM-48+pseudoboehmite) for the synthesis of benzene through methylcyclopentane shows that pseudoboehmite increases the total amount of acid sites and weakens the acid strength, compared to those of the Pt/HZSM-48 catalyst. Lewis acid sites were more abundant than Brönsted acid sites over the Pt/(HZSM-48+pseudoboehmite) catalysts resulting in the increase of selectivity to the ring-enlargement reaction over to the ring-opening reaction 3 . It is difficult to overestimate the importance of alumina in today's catalysis.…”

“…This procedure is performed, specifying the factor to be studied and assigning to it, +1 coefficients, for higher levels and -1, for lower levels. A two-level factorial design for the study of three variables is represented as 2 3 , resulting in *e-mail: ahmunhoz@yahoo.com eight tests arranged in a matrix of experiments. Thus, after a statistical calculation of the effects, it is possible to interpret the influences and / or interactions of the variables studied in the experimental process 14,15 .…”