A Comparative Ab Initio Study of Anhydrous Dehydrogenation of Linear-Chain Alcohols on Cu(110)

Abstract

The catalytic behavior of Cu surfaces in the anhydrous production of aldehydes from alcohols, a process of industrial significance, is puzzling: the two simplest alcohols (methanol and ethanol) show dramatically different decomposition behavior on Cu. Here, we study the thermodynamic and kinetic processes involved in the anhydrous dehydrogenation of linear-chain alcohols including methanol, ethanol, 1-propanol, and 1-butanol on the Cu(110) surface using multiscale approaches. First, we obtain the adsorption structures and energies of the reaction intermediates, in which van der Waals (vdW) interactions play a crucial role. Then, we determine the kinetic barriers for the two dehydrogenation steps, namely, the O−H and the subsequent C−H bond-breaking on Cu. The reaction of methoxy-to-formaldehyde has a rather high-energy transition state, in contrast to that of alkoxide-to-aldehyde in the longer-chain systems. This difference qualitatively explains the lower production efficiency of formaldehyde on Cu. Finally, we simulate the production rates of aldehydes based on which we optimize reaction conditions and propose possible avenues for enhancing the production of anhydrous formaldehyde using Cu-based catalysts.

Effect of Frustrated Rotations on the Pre-Exponential Factor for Unimolecular Reactions on Surfaces: A Case Study of Alkoxy Dehydrogenation

“…In previous work the lowest energy structure for each alkoxide was determined. 6 These structures were confirmed to be stable/metastable by harmonic frequency analysis.…”

“…The configurations of methoxy and ethoxy remain unchanged compared to those previously reported. 6 The newly discovered structures were more stable by 0.02 and 0.08 eV/molecule for 1-propoxy and 1-butoxy, respectively. Such energy stabilization is associated with the variation in the orientation of the molecule tail with respect to the β-C-O axis.…”

“…The NEB calculations suggested that the transition It is important to emphasize more generally the difficulty in finding the global minimum in the high-dimensional configuration space of adsorption for large molecules. The searching strategy used previously for these alkoxides, 6 in which the molecule was considered as a rigid body and different adsorption sites and orientations of the molecule around its chemical bond with the surface were probed, may not be sufficient to find the structure at the global minimum energy because bending in the molecular skeleton and rotation around its internal bonds (torsion), which are common for adsorbed molecules, are extremely difficult to fully sample for large molecules. The abundance of local basins, potentially with multiple configurations with near-degenerate energies highlight the difficulty to find the global minimum for an accurate estimation of kinetic parameters and other statistical quantities, such as activation energy, entropy, and pre-exponential factor.…”

Catalytic Effect of Hydrogen Bond on Oxhydryl Dehydrogenation in Methanol Steam Reforming on Ni(111)

“…Also based on DFT calculations, Krajčí et al demonstrated the CO/CO 2 selectivity of MSR on many alloys, e.g., PdZn, PtZn and NiZn [13]. Chen et al [14], Lausche et al [15], and Kramer et al [16] studied the selectivity of the dehydrogenation of methanol on Cu(110), Ni(100) and Ni(111), respectively. MSRs on Pt [16], Pd [16], Pt 3 Ni alloy [17], Pt-Skinned PtNi Bimetallic Clusters [18] and Co [19] have also been investigated.…”

An AIMD study of dissociative chemisorption of methanol on Cu(111) with implications for formaldehyde formation

“…For example, experimental evidence for formaldehyde formation on copper catalysts through direct decomposition of methanol exists [2][3][4][5] , although the underlying pathways remain unclear. So far, theoretical calculations have only been able to deal with this reaction scheme on a static level using transition state theory [6][7][8][9][10][11][12] or a dynamical level but with a frozen surface 13 . However, these levels of theory exclude exchange of energy between the surface and the molecule and transition state theory excludes any dynamical effects such as steering as well.…”