A Systematic Study of Methylation from Benzene to Hexamethylbenzene in H-SSZ-13 Using Density Functional Theory and Ab Initio Calculations

Abstract

Methylation of aromatic molecules in H-SSZ-13 is studied from benzene to hexamethylbenzene via all possible isomers. Both methylations with methanol (MeOH) and dimethyl ether (DME) are investigated via both stepwise and concerted mechanisms. Calculations are carried out using periodic density functional theory corrected by high-level DLPNO-CCSD­(T) calculations on cluster models. While we find little selectivity between the methylations of different aromatics, our calculations indicate that isomerization via methyl shifts between different isomers is a viable mechanism with barriers comparable to methylation. The generally observed trend is that MeOH methylation barriers are smaller than those using DME, with the difference between MeOH and DME increasing with the level of methylation of the aromatic molecule.

Theoretical investigation of the side-chain mechanism of the MTO process over H-SSZ-13 using DFT and ab initio calculations

“…This choice is motivated by our earlier work that identified HMB, PMB, and TMBs as the thermodynamically most stable species adsorbed in H-SSZ-13 under typical reactions of the MTO process. 65 Similar observations have been made for the Fig. 1 (a) Schematics of the various reaction steps of the studied side-chain methylation of the MTO process with HMB acting as the co-catalyst.…”

“…6,[8][9][10][11][12][13][14]30 This is highly interesting both from a conceptual but also practical point of view, as the selectivity towards lighter olefins might significantly differ for these two cycles. 37,38 For the aromatic cycle, in addition to the methylation of aromatics, [57][58][59][60][61][62][63][64][65] there are two main mechanistic proposals, the side-chain and the paring mechanisms shown in Scheme 1. 7,17,18,[66][67][68] In the paring mechanism, the C6 ring is contracted to a C5 ring, shaving off the olefin.…”

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

“…Density functional theory (DFT) calculations are increasingly employed to gain insight into the reactivity of zeolites [16][17][18][19][20][21], for methanol dehydration [22][23][24][25] as well as subsequent steps in the MTO process involving the reaction of olefins and aromatics [26][27][28][29][30][31][32][33][34]. Kinetic models were developed to study initiation, step-wise methylation via surface methoxy species (SMS), concerted methylation, cracking and deactivation through coking revealing many features of the process [35][36][37][38][39].…”

Influence of Confinement on Barriers for Alkoxide Formation in Acidic Zeolites

“…[11][12][13][14][15] A detailed understanding of how the effect of confinement influences the activity and selectivity of dehydration reactions related to these conversions is therefore highly desirable. Density functional theory (DFT) calculations offer a useful tool to investigate the reaction mechanisms and the intrinsic effect of the confinement in great detail [16][17][18][19][20][21][22] and to deduct trends from one material to another. [23][24][25][26] DFT calculations also help understanding, how electronic and steric effects influence reaction barriers and adsorption energies within zeolite pores.…”

“…A detailed understanding of how the effect of confinement influences the activity and selectivity of dehydration reactions related to these conversions is therefore highly desirable. Density functional theory (DFT) calculations offer a useful tool to investigate the reaction mechanisms and the intrinsic effect of the confinement in great detail [16–22] and to deduct trends from one material to another [23–26] …”