Synthesis optimization of mesoporous ZSM-5 through desilication-reassembly in the methanol-to-propylene reaction

Preparation of hierarchical H-[B]-ZSM-5 zeolites by a desilication method as a highly selective catalyst for conversion of methanol to propylene

“…The existence of some broken crystals in the alkalitreated catalysts can be interpreted by the dissolution of zeolite crystals as well as framework destruction. Similar results have been obtained by other researchers after desilication of ZSM-5 zeolites (Gorzin et al 2018(Gorzin et al , 2019aAkyalcin et al 2019;Rahmani and Taghizadeh 2017). One of the advantages of the desilicated catalysts is having open pores that facilitate mass transfer and enhance the catalytic activity in the MTP reaction, which will be presented further.…”

“…This enhancement in acidity is caused by the enhanced Al content, a fact that can be related to a more selective desilication when alkaline treatment at standard conditions is carried out. The increment in the aluminum for specimens that underwent alkaline treatment was also previously reported in the literature (Ahmadpour and Taghizadeh 2015b;Sadowska et al 2013b;Akyalcin et al 2019;Rahmani and Taghizadeh 2017;Tzoulaki et al 2012;Góra-Marek et al 2014). The stability of the specimens and selectivity of the light olefin cut in the MTP process isstrongly dependent on the suitable acid site content.…”

“…It is believed that converting methanol to hydrocarbons on ZSM-5 zeolites consists of three main steps: the first step is the fast water loss of methanol to form DME, which occurs predominantly on the weak acid sites. In the second and third stages, methanol and dimethyl ether are converted initially into light olefins and subsequently transformed into heavier hydrocarbons (olefins, paraffins, and aromatics) on the strong acid sites (Rahmani and Taghizadeh 2017). In the solid-acid catalytic reaction, the acidity of the catalyst is among the most significant reasons causing effects in the reactivity in the MTP reaction.…”

“…In addition to participating actively while converting methanol to dimethyl ether, the weak acidity (Lewis acidity) is capable of catalyzing the alkylation and methylation reactions as well, which affect the propylene selectivity considerably, based on the dual-cycle notion (Yaripour et al 2015;Javdani et al 2019;Khanmohammadi et al 2016;Wu and Weitz 2014;Weitkamp 2000;Matsuoka et al 2017). Besides, the weak acid sites extensively prohibit different hydrogen-transfer reactions that generate saturated hydrocarbons (methane, ethane, propane, and the like) and aromatics ( C + 5 ) that act as the precursors for the generation of coke (Yaripour et al 2015;Ahmadpour and Taghizadeh 2015b;Chen et al 2015;Rahmani and Taghizadeh 2017;Javdani et al 2019;Feng et al 2018a;Bjørgen et al 2007). As a result Table 3, in comparison to the parent H-[B]-ZSM-5 catalyst, the alkali-treated sample (Des-8) with higher weak acid site content and lower strong acid site content is an index of a favorable strong/week acid ratio (0.69) for the olefin-based cycle of the MTP process to propagate, causing considerably more propylene selectivity for a longer period.…”

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…[88] CTAB with NaOH is another alternative that can be used during dissolution and recrystallization. [89] It was used by Subhan et al, showing the formation of mesostructures similar to Al-MCM-41, with enhanced adsorptive desulfurization properties. [90] The dissolution-recrystallization approach can also be combined with other synthesis techniques.…”