Adsorption of acetic acid and methanol on H-Beta zeolite: An experimental and theoretical study

Molecular‐level Understanding of the Rate‐determining Step in Esterification Reactions Catalyzed by H‐ZSM‐5 Zeolite. An Experimental and Theoretical Study

“…The first process commences above 63 °C and extends to 253 °C with a maximum at 180 °C, and is related to the desorption of physically adsorbed AcOH molecules on silanol groups and BAS by hydrogen bonding interactions. This is in line with previous results for desorption of AcOH on H‐β . The desorbed gases of the surface (Fig.…”

“…The first one related to physisorbed MeOH on the H‐ZSM‐5 (between 50–206 °C). Second process occurs between 206 °C and 275 °C, and it refers to a chemical adsorption and, hence, methanol dehydration followed by thermal degradation of the chemisorbed methanol, other authors using MFI zeolite proposed that during the desorption/reaction process (between 127–177 °C) most of the protonated MeOH is desorbed without reacting, however over 227 °C the increase in hydrocarbon formation could indicate the beginning of the autocatalytic step in the MeOH conversion, results similar to those found for H‐β …”

“…These results were attributed to the formation of a strongly adsorbed species on the acidic surface, characterizing the presence of organic intermediates as chemisorbed methoxide formed during the reaction, and gradually at higher temperatures the mass loss caused by the thermal degradation (combustion) of the formed products. The same process was observed in H‐β but at 270 °C, showing that the AcOH adsorption in H‐ZSM‐5 was weaker probably due the ratio of the active sites by mass (m 2 g − 1 ).…”

“…Previous studies for H‐β under the same TGA‐IR conditions showed different results when compared to H‐ZSM‐5, we consider that the deposition of carbon related to the adsorption of AcOH at high temperatures is intrinsically linked with the strength of the active sites and the mass transfer (pore diameter of H‐β vs H‐ZSM‐5) of the products formed inside the channels, contributing for the greater formation of coke. Mass loss curves (TGA‐dTG, Figure ) report during sample heating (AcOH and MeOH) at 650 °C, that the adsorption of AcOH over H‐ZSM‐5 is similar in H‐β, but is clearly observed by EGA the presence of CO at high temperatures which indicates a strong adsorption of organic molecules inside the pores of H‐ZSM‐5.…”

“…by using kinetic measurements, postulated that a surface acetic acid/ethanol complex is involved in the rate‐determining reaction step of esterification reactions on H‐zeolites . Thus, in order to obtain more information about the mechanism, in our previous work, we discussed and studied the adsorption of AcOH and MeOH on H‐β as a model of reaction of the initial step of the esterification reaction . Results showed that the adsorption of acetic acid by the carbonyl group is more favorable when compared to the adsorption of methanol in a single reaction step in a three‐dimensional structure, additionally we proposed a revised mechanism involving the acetic acid/methanol adsorbed complex.…”