First-Principles Kinetic Study on the Effect of the Zeolite Framework on 1-Butanol Dehydration

Abstract

Understanding the role of zeolite topology in defining its catalytic performance is of prime importance for the development of catalytic processes. Herein, a first-principles-based microkinetic study of 1-butanol dehydration is used to illustrate the effect of different zeolites (i.e., H-FAU, H-ZSM-5, H-ZSM-22, and H-FER) on the dehydration activity and product selectivity. Under identical reaction conditions, microkinetic simulations show significant variation in dehydration rates and butene/ether selectivity profiles within the different zeolites. H-ZSM-5 has the highest catalytic activity, whereas H-FAU and H-FER exhibit a higher butene selectivity. In the large pore H-FAU, the weaker dispersive stabilization of the dimer makes the butene formation by monomolecular direct dehydration via a concerted anti elimination compete with di-n-butyl ether formation. In H-FER, steric constraints due to partial confinement of the protonated di-n-butyl ether in the 8-MR channel decrease its stability, favoring its further decomposition to butene via a concerted syn elimination of butanol. On the other hand, the higher ether selectivity in H-ZSM-5 and H-ZSM-22 is rationalized on the basis of a higher stability for adsorbed ether and a higher activation barrier for ether decomposition. In addition to the effect of the zeolite framework, this study further highlights the pivotal role of the reaction conditions in determining the most abundant reaction intermediate, dominant reaction paths, and underlying reaction mechanisms. In general, for all four zeolites, an increase in reaction temperature and a decrease in butanol feed partial pressure favors direct dehydration of butanol to butene (via butanol monomer). However, a decrease in reaction temperature and increase in butanol feed partial pressure favors dimer-mediated dibutyl ether formation. An increase in conversion favors direct dehydration and dibutyl ether decomposition to butene.

Surface chemistry dictates stability and oxidation state of supported single metal catalyst atoms

“…Based on the microkinetic information of the previous section and the reaction scheme shown in Fig. 2, analytical rate expressions can be derived 30 following an analysis similar to the one described by John et al 31 These are the so-called a posteriori or expert knowledge-based reduced models, i.e., they use microkinetic (expert) knowledge to carry out the reduction without making a priori assumptions as in standard (textbook) Langmuir-Hinshelwood rate expressions. [32][33][34][35][36] These can be validated against the full microkinetic model (see Fig.…”

Study of n-butanol conversion to butenes: Effect of Si/Al ratio on activity, selectivity and kinetics

“…Prior work suggests the same reaction mechanism holds for a range of acidic zeolites on the dehydration of alcohols. This could open the possibility to construct a single micro-kinetic model enabling the description of the catalytic performance of a range of zeolites [32].…”

“…The difference in selectivity and activity of the various zeolites is proposed to be related to a change in dominant surface species and pathways, rather than a change in reaction mechanism. These effects on selectivity and activity are caused by a different interaction of the lattice with the formed intermediates and surface species, which can be related to Gibbs free energies of intermediates and/or transition states considered in the micro-kinetic model [32]. The general reaction scheme for 1-butanol dehydration ( Figure 1) is assumed to be a parallel-consecutive pathway consisting of the direct dehydration of 1-butanol to 1-butene (path A) and an ether-mediated conversion of 1-butanol towards 1-butene (path B + C) [24,33,34].…”

“…This parameter is used to account for the number of active sites available in the reactor and is determined as (W.Ca)/F 0 with W the catalyst mass, Ca the number of catalytic sites per gram of catalyst and F 0 the initial flowrate of the reactant. In this way the effect of the varying number of active sites per gram of catalyst with a change in Si/Al ratio can be excluded by activities at identical site times [32,[34][35][36].…”

Catalysis-in-a-Box: Robotic Screening of Catalytic Materials in the Time of COVID-19 and Beyond

“…Error bars in (A) to (C) represent the 95% CI on multiple injections from the same experimental run to measure steady-state rates; error bars in (D) represent 95% CI on replicate independent measurements on fresh/recalcined catalyst beds. The references indicated in the insets 38 , 40 , 44 , [45 , 46 , 47 , 48 , 49 , 50 are also listed in the last column of Table 1 . …”