Beta-MCM-41 micro-mesoporous catalysts in the hydroisomerization of n-heptane: Definition of an indexed isomerization factor as a performance descriptor

Abstract

Beta-MCM-41(BM) composites consisting of Beta zeolite grown on MCM-41 type mesoporous structure were prepared. The composite materials were used as a support for stabilization of Pt. The Pt containing catalysts (Pt/HBM) were applied in nheptane hydroisomerization reaction. The Pt/HBM catalysts showed higher n-heptane conversion and higher selectivity to isoheptanes in comparison to pure Beta and MCM-41. The results were explained by the accelerated diffusion of isoheptanes in the Pt/HBM composites, and the high concentration of acid sites with a moderate strength in the composites, which reduced the cracking of reactants and products. Based on the experimental results, an indexed isomerization factor (IIF) was deduced, which is correlated with the physical properties of the supports. The results indicated that the isoheptane yield of the catalysts is strongly dependent on the support (IIF). The general IIF descriptor for predicting the isomerization performance of support materials can provide precise guidance for the design of new micro-mesoporous composites.

Beneficial use of ultrasound irradiation in synthesis of beta–clinoptilolite composite used in heavy oil upgrading process

“…Beta/CLT sample XRD pattern displays both crystalline phases of clinoptilolite and beta zeolite indicating the coexistence of both phases in the physical mixture of beta and clinoptilolite, meanwhile, no new peak is observed. Intensities of all the peaks have decreased compared to their parents, CLT and Beta, which is in line with results of Gao et al 30 in which, diffraction peaks have lower intensities aer making a physical mixture of Beta-MCM-41.…”

“…Peaks located between these regions are assigned to moderate-strong acidic sites in the samples. 30 Different values of acidities for each sample, based on the amount of desorbed ammonia were calculated from desorption peak areas and are presented in Table 4.…”

“…29,50 High concentration of weak and moderate acidic sites on Beta, which prevents over cracking of products and reactants, is the reason of higher selectivity of this zeolite to intermediate cracking products in heavy oil upgrading. 30 CLT sample has also three distinct peaks at 126 C, 337 C and 654 C. It has been proposed that high temperature peak is associated to the framework Al atoms which induce strong acidity, while low temperature peak represents weak acid sites ascribed to nonframework Al atoms. 54,55 Natural zeolite used in this research has a Si/Al ratio equal to 5.66, which indicates the presence of high amount of framework Al atoms inducing strong acidity in the zeolite.…”

“…24,25 Different composites of zeolite beta have been synthesized for different intentions, for example it has been used in beta/Y composite in order to benet from larger pore openings of beta zeolite coupled with high acidity of Y zeolite, 26,27 or in beta/MCM-41 composite to induce larger mesopore volume attained from mesoporous structure of MCM-41 aluminosilicate paired with moderate acidity of zeolite beta. [28][29][30] Therefore, beta zeolite has potential to be paired with different kinds of zeolites in a composite.…”

“…Zeolite composites may be synthesized by different methods such as crystallization process, seeding, hydrothermal synthesis, core shell structure, etc. 30 However, these methods have many determining parameters such as temperature, alkaline environment, exact ratios of precursors and long synthesis times, which makes it difficult to have complete control over the synthesis procedure. Physical mixing is the easiest way to prepare a mixture of two zeolites.…”