Highly Selective Activation of C–H Bond and Inhibition of C–C Bond Cleavage by Tuning Strong Oxidative Pd Sites

Abstract

Improving the product selectivity meanwhile restraining deep oxidation still remains a great challenge over the supported Pd-based catalysts. Herein, we demonstrate a universal strategy where the surface strong oxidative Pd sites are partially covered by the transition metal (e. g., Cu, Co, Ni, and Mn) oxide through thermal treatment of alloys. It could effectively inhibit the deep oxidation of isopropanol and achieve the ultrahigh selectivity (>98%) to the target product acetone in a wide temperature range of 50–200 °C, even at 150–200 °C with almost 100% isopropanol conversion over PdCu1.2/Al2O3, while an obvious decline in acetone selectivity is observed from 150 °C over Pd/Al2O3. Furthermore, it greatly improves the low-temperature catalytic activity (acetone formation rate at 110 °C over PdCu1.2/Al2O3, 34.1 times higher than that over Pd/Al2O3). The decrease of surface Pd site exposure weakens the cleavage for the C–C bond, while the introduction of proper CuO shifts the d-band center (εd) of Pd upward and strengthens the adsorption and activation of reactants, providing more reactive oxygen species, especially the key super oxygen species (O2 –) for selective oxidation, and significantly reducing the barrier of O–H and β-C–H bond scission. The molecular-level understanding of the C–H and C–C bond scission mechanism will guide the regulation of strong oxidative noble metal sites with relatively inert metal oxide for the other selective catalytic oxidation reactions.

Separated Active Site and Reaction Space for Multi‐Pollutant Elimination Significantly Enhancing Low Toxic Product Selectivity

“…In order to understand the mechanism of C─Cl bond cleavage during CB oxidation, the densities of states (DOS) were examined related to CB adsorption on RuO 2 (110) (Figure 4c). [49,50] The energy levels of the Ru d orbitals near the Fermi level and the CB 𝜋* orbitals (LUMO) were compatible, resulting in the partial occupation of the newly formed d-𝜋* orbitals. According to this bonding model, the partially empty 𝜋* orbitals of the CB molecule received electrons from the metal d orbitals, thereby weakening the C─Cl bond and causing the CB molecule to have a radial nature (including an unpaired electron), which made it reactive toward dehydrogenation.…”

Pt1Bi1 Intermetallic Structure with Controllable C–H and C–O Bond Activation Ability for Enhanced Diethylene Glycol Oxidation

“…Such bimetallic catalysts display unique geometry coordination environments and electronic structures that are different from the parent Pt metal. − In particular, Pt-based intermetallic compounds (IMCs), such as the tetragonal L10-type PtM with heterometal atoms bonded, can be varied to a limited extent while still maintaining a highly structured lattice structure with a large number of interatomic bonding bonds, accompanied by a strong d–d orbital interaction. − Therefore, they have been widely used in polyol oxidation and CO 2 hydrogenation reactions. − For instance, Feng et al found that the introduction of Bi to Pt can induce the formation of a Pt–Bi active structure, promoting selective oxidation of the C–H bond on glycerol. Guo et al reported that reducing the exposure of surface Pd sites by introducing Cu maintains the high C–H bond activation ability and simultaneously inhibits the C–C bond cleavage for the oxidation of isopropanol to acetone. Obviously, the Pt-based IMC shows great potential in achieving the desired activation of the C–H bond and preventing the nonselective activation of the C–O–C bond.…”

Ruthenium–Cobalt Solid-Solution Alloy Nanoparticles for Enhanced Photopromoted Thermocatalytic CO2 Hydrogenation to Methane

“…Solid-solution alloy nanoparticles with atomic-scale homogeneity hold significant potential for maximizing catalytic activity and optimizing selectivity in comparison with their monometallic counterparts owing to the synergistic contributions from constituent elements. − In these systems, the electronic structure can be finely regulated by successively tuning the composition of alloy nanoparticles, which results in the alteration of binding energies of reactants/intermediates onto the catalyst surfaces. − Consequently, the catalytic efficiency toward a specific reaction could be promoted by accelerating the rate-determining step along the reaction pathway . Recently, the incorporation of nonprecious transition-metal elements into noble metals forming alloys with the aim to reduce cost and simultaneously enhance catalytic performance has become a cutting-edge research frontier, and the successful preparation of PtFe, RhCu, PtCo, and AuCu with superior catalytic behaviors relative to the monometallic precious metal-based catalysts have elaborated the potential of this strategy.…”