Guidelines to Achieving High Selectivity for the Hydrogenation of α,β-Unsaturated Aldehydes with Bimetallic and Dilute Alloy Catalysts: A Review

Abstract

Selective hydrogenation of α,ß-unsaturated aldehydes to unsaturated alcohols is a challenging class of reactions, yielding valuable intermediates for the production of pharmaceuticals, perfumes, and flavorings. On monometallic heterogeneous catalysts, the formation of the unsaturated alcohols is thermodynamically disfavored over the saturated aldehydes. Hence, new catalysts are required to achieve the desired selectivity. Herein, the literature of three major research areas in catalysis is integrated as a step toward establishing the guidelines for enhancing the selectivity: reactor studies of complex catalyst materials at operating temperature and pressure; surface science studies of crystalline surfaces in ultrahigh vacuum; and first-principles modeling using density functional theory calculations. Aggregate analysis shows that bimetallic and dilute alloy catalysts significantly enhance the selectivity to the unsaturated alcohols compared to monometallic catalysts. This comprehensive review focuses primarily on the role of different metal surfaces as well as the factors that promote the adsorption of the unsaturated aldehyde via its C=O bond, most notably by electronic modification of the surface and formation of the electrophilic sites. Furthermore, challenges, gaps, and opportunities are identified to advance the rational design of efficient catalysts for this class of reactions, including the need for systematic studies of catalytic processes, theoretical modeling of complex materials, and model studies under ambient pressure and temperature.

Edge‐Confined Pt1/MoS2 Single‐Atom Catalyst Promoting the Selective Activation of Carbon‐Oxygen Bond

“…H 2 activation is considered as the crucial factor in determining the overall catalytic activity for this family of reactions [24,41,42] . The electron depletion of the edge‐confined Pt 1 atoms enables to induce downshift of the d ‐band center of the Pt δ+ species (0<δ<2) when comparing with the metallic Pt species and consequently reduces the bonding strength of the dissociated H species, [43,44] which enables to enhance the catalytic activity of dissociated H species.…”

“…H 2 activation is considered as the crucial factor in determining the overall catalytic activity for this family of reactions. [24,41,42] The electron depletion of the edge-confined Pt 1 atoms enables to induce downshift of the d-band center of the Pt δ + species (0 < δ < 2) when comparing with the metallic Pt species and consequently reduces the bonding strength of the dissociated H species, [43,44] which enables to enhance the catalytic activity of dissociated H species. The XPS valence band results further confirm that the location of d-band center of Pt 1 /MoS 2 SAC (ɛ d = À 3.95 eV) moves further away from the Fermi level compared with that of nano-Pt/MoS 2 (ɛ d = À 3.26 eV) as shown in Figure S9.…”

Exploring paths of chemical transformations in molecular and periodic systems: An approach utilizing force

“…Those paths help to elucidate not only how atoms and bonds are rearranged but also how much energy is required during the corresponding transformation, which then provide deep insights into the corresponding chemical transformations themselves. Therefore, the paths of chemical transformations have been calculated in many theoretical studies 1–8 …”

Formation of a Ti–Cu(111) single atom alloy: Structure and CO binding

“…For instance, the high oxophilicity of early transition metals could lead to preferential activation and functionalization of O-containing functional groups of organic compounds, enabling chemistries such as the selective hydrogenation of unsaturated aldehydes to alkenols. 13 Recent calculations using density functional theory (DFT) also predict that several early transition metal SAAs are capable of activating CH 4 at low temperature. 4 This prediction suggests possibilities for selectively converting alkanes to value-added products since the ability to activate alkane C-H bonds under mild conditions, particularly at an isolated site, can suppress extensive decomposition of the alkane.…”