Multiple potential active sites on the surface of γ-Al2O3 have led to debate about the role of Lewis and/or Bronsted acidity in reactions of ethanol, while mechanistic insights into competitive production of ethylene and diethyl ether are scarce. In this study, elementary adsorption and reaction mechanisms for ethanol dehydration and etherification are studied on the γ-Al2O3(100) surface using density functional theory calculations. The O atom of adsorbed ethanol interacts strongly with surface Al (Lewis acid) sites, while adsorption is weak on Bronsted (surface H) and surface O sites. Water, a byproduct of both ethylene and diethyl ether formation, competes with ethanol for adsorption sites. Multiple pathways for ethylene formation from ethanol are explored, and a concerted Lewis-catalyzed elimination (E2) mechanism is found to be the energetically preferred pathway, with a barrier of Ea = 37 kcal/mol at the most stable site. Diethyl ether formation mechanisms presented for the first time on γ-Al2O3 indi...

Density Functional Theory-Computed Mechanisms of Ethylene and Diethyl Ether Formation from Ethanol on γ-Al2O3(100)

Cu/boehmite: A highly active catalyst for hydrogenolysis of glycerol to 1,2-propanediol

We examine the heterogeneity of the Lewis acidity on the (100) and (110) facets of γ-Al2O3 by computing the binding energies of various oxygenates, in addition to the reaction barriers of dehydration and etherification reactions of ethanol. We show that the ethanol dehydration barrier is moderately affected by site heterogeneity (barriers between 1.2 and 1.6 eV); in contrast, a nearly 3-fold change in the ethanol etherification barrier is found among the various Al3+ sites. In order to rationalize these results, the s-conduction band mean of the Al3+ sites is introduced as a descriptor to characterize the ability to transfer electron charge from the adsorbate to the Lewis acid site. It is shown for the first time that this descriptor quantitatively correlates the oxygenate binding energies and the ethanol dehydration reaction barriers. However, for the ethanol etherification reactions the s-conduction band mean of the Al3+ sites describes barriers only qualitatively due to the bimolecular nature of this r...

Site-Dependent Lewis Acidity of γ-Al2O3 and Its Impact on Ethanol Dehydration and Etherification

A detailed and in-depth study of the deactivation of Pt and/or Ni-based γ-Al 2 O 3 catalysts prepared by impregnation and acid and basic sol–gel methods, previously tested in glycerol aqueous phase reforming (APR) for H 2 production, has been made. The aim has been to get a further and advanced understanding of the factors behind this deactivation. Accordingly, all the used catalysts were systematically characterized by appropriate techniques, such as ICP-AES, XRD, XPS and TG/DGT-O 2 . Some used samples were also examined by BET, TPD-NH 3 , TPR-H 2 and TEM. The characterization results corroborate the following: (i) a significant part of γ-Al 2 O 3 in sol–gel catalysts was structurally transformed into γ-AlOOH, changing their textural properties, such as surface area and porosity, surface acidity and metal dispersion, and (ii) the Ni metallic particles in the impregnated catalysts underwent major agglomeration, while the Ni particles in the sol–gel counterparts were more affected by re-oxidation phenomena. Data obtained by ICP-AES and thermal analysis indicate, respectively, that Pt and Ni phase leaching and the formation of highly graphitized coke were negligible. However, some adsorption of carbonaceous molecular species has been detected on some catalysts. All these observations clearly confirm that the metallic and acid active sites of Pt and/or Ni–based γ-Al 2 O 3 catalysts experimented quantitative and qualitative modifications during the glycerol APR process that compromised their catalytic performances.

Deactivation study of the Pt and/or Ni-based γ-Al2O3 catalysts used in the aqueous phase reforming of glycerol for H2 production

Boehmite (γ-AlOOH) and gibbsite (α-Al(OH)3) are important archetype (oxy)hydroxides of aluminum in nature that also play diverse roles across a plethora of industrial applications. Developing the a...

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Boehmite and Gibbsite Nanoplates for the Synthesis of Advanced Alumina Products

The influence of the liquid environment on the reaction mechanism in slurry reactors has not been fully investigated. In this work, dimethyl ether (DME) synthesis from methanol dehydration over γ-Al 2 O 3 (1 1 0) and AlOOH (1 0 0) in liquid paraffin and in the gas phase is studied using density functional theory combined with the conductor-like solvent model. The liquid paraffin can influence surface relaxation, Mulliken charges, and adsorptive behavior of γ-Al 2 O 3 and AlOOH. For DME synthesis, liquid paraffin does not influence the reaction path over the γ-Al 2 O 3 surface, but influences its activation energy. Liquid paraffin influences the activation energy and also alters the reaction path of DME synthesis over AlOOH

Zhe Li

Papers

Theoretical studies on the reaction mechanisms of AlOOH- and γ-Al2O3-catalysed methanol dehydration in the gas and liquid phases