Unoccupied states and charge transfer in Cu-Pd alloys studied by bremsstrahlung isochromat spectroscopy, x-ray photoelectron spectroscopy, and LIII absorption spectroscopy

Electron Divergence of Cuδ- and Pdδ+ in Cu3Pd Alloy-Based Heterojunctions Boosts Concerted C≡C Bond Binding and the Volmer Step for Alkynol Semihydrogenation

Electrocatalytic semihydrogenation of alkynols presents a sustainable alternative to conventional thermal methodologies for the high-value production of alkenols. The design of efficient catalysts with superior catalytic and energy efficiency for semihydrogenation poses a significant challenge. Here, we present the application of an electron-divergent Cu3Pd alloy-based heterojunction in promoting the electrocatalytic semihydrogenation of alkynols to alkenols using water as the proton source. The tunable electron divergence of Cuδ- and Pdδ+, modulated by rectifying contact with nitrogen-rich carbons, enables the concerted binding of active H species from the Volmer step of water dissociation and the C≡C bond of alkynols on Pdδ+ sites. Simultaneously, the pronounced electron divergence of Cu3Pd facilitates the universal adsorption of OH species from the Volmer step and alkynols on the Cuδ- sites. The electron-divergent dual-center substantially boosts water dissociation and inhibition of completing hydrogen evolution to give a turnover frequency of 2412 h-1, outperforming the reported electrocatalysts' value of 7.3. Moreover, the continuous production of alkenols at industrial-related current density (-200 mA cm-2) over the efficient and durable Cu3Pd-based electrolyzer could achieve a cathodic energy efficiency of 45 mol kW·h-1, 1.7 times the bench-marked reactors, promising great potential for sustainable industrial synthesis.

Fabrication of a PdCu@SiO2@Cu core-shell-satellite catalyst for the selective hydrogenation of acetylene

Pd25Cu75@SiO2 core-shell and PdCu@SiO2@Cu core-shell-satellite architectures were fabricated by silica-coating of Pd25Cu75 colloids in a reverse microemulsion. Hydrolysis of tetraethylorthosilicate in the reverse microemulsion containing hydrazine and ammonia yielded a core-shell structure, while the use of ammonia only, instead of a mixture of hydrazine and ammonia, formed a core-shell-satellite structure. The ammonia-leached copper species migrated onto the developing silica shell and formed smaller Cu clusters. Air-calcination at 673 K followed by H2-reduction at 773 K of the as-synthesized samples removed the organic surfactants and generated the permeable porous silica shells. The core-shell catalyst consisted of a metal core (8.5 nm) and a silica shell (7.8 nm), while the core-shell-satellite catalyst was composed by a metal core (7.0 nm), a silica shell (8.0 nm), and satellite Cu clusters (1.4 nm) on the silica shell. When used to catalyze the selective hydrogenation of acetylene to ethylene, the core-shell-satellite catalyst showed substantially enhanced activity and stability because of the synergetic catalysis between the metal core and the surrounding Cu clusters.

Contrasting Capability of Single Atom Palladium for Thermocatalytic versus Electrocatalytic Nitrate Reduction Reaction

The occurrence of high concentrations of nitrate in various water resources is a significant environmental and human health threat, demanding effective removal technologies. Single atom alloys (SAAs) have emerged as a promising bimetallic material architecture in various thermocatalytic and electrocatalytic schemes including nitrate reduction reaction (NRR). This study suggests that there exists a stark contrast between thermocatalytic (T-NRR) and electrocatalytic (E-NRR) pathways that resulted in dramatic differences in SAA performances. Among Pd/Cu nanoalloys with varying Pd-Cu ratios from 1:100 to 100:1, Pd/Cu(1:100) SAA exhibited the greatest activity (TOFPd = 2 min-1) and highest N2 selectivity (94%) for E-NRR, while the same SAA performed poorly for T-NRR as compared to other nanoalloy counterparts. DFT calculations demonstrate that the improved performance and N2 selectivity of Pd/Cu(1:100) in E-NRR compared to T-NRR originate from the higher stability of NO3* in electrocatalysis and a lower N2 formation barrier than NH due to localized pH effects and the ability to extract protons from water. This study establishes the performance and mechanistic differences of SAA and nanoalloys for T-NRR versus E-NRR.

Progress and perspective for conversion of plastic wastes into valuable chemicals

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Improved H2 utilization by Pd doping in cobalt catalysts for reductive amination of polypropylene glycol

Cobalt based catalysts having enhanced H2 dissociation and desorption were synthesized by inserting a trace amount of palladium. These catalysts were used for the reductive amination of polypropylene glycol (PPG) to polyetheramine (PEA). The catalytic activity toward PEA was significantly increased by incorporating an extremely low content of palladium (around 0.01 wt%) into cobalt based catalysts. The Pd inserted cobalt catalysts promoted reduction of cobalt oxide to cobalt metal and inhibited formation of cobalt nitride in the reductive amination. The Pd inserted cobalt catalysts not only enhanced hydrogen dissociation but also accelerated hydrogen desorption by increasing the electron density of cobalt through interaction between cobalt and palladium. These play a critical role in reducing cobalt oxide or cobalt nitride to cobalt metal as an active site for the reductive amination. Thus, the Pd inserted cobalt catalysts provide improved catalytic performance toward PEA production by maintaining the cobalt metal state.

Optimising surface d charge of AuPd nanoalloy catalysts for enhanced catalytic activity

Understanding the catalytic mechanism of bimetallic nanocatalysts remains challenging. Here, we adopt an adsorbate mediated thermal reduction approach to yield monodispersed AuPd catalysts with continuous change of the Pd-Au coordination numbers embedded in a mesoporous carbonaceous matrix. The structure of nanoalloys is well-defined, allowing for a direct determination of the structure-property relationship. The results show that the Pd single atom and dimer are the active sites for the base-free oxidation of primary alcohols. Remarkably, the d-orbital charge on the surface of Pd serves as a descriptor to the adsorbate states and hence the catalytic performance. The maximum d-charge gain occurred in a composition with 33-50 at% Pd corresponds to up to 9 times enhancement in the reaction rate compared to the neat Pd. The findings not only open an avenue towards the rational design of catalysts but also enable the identification of key steps involved in the catalytic reactions.

CO adsorption on Cu–Pd alloy surfaces: ligand versus ensemble effects

The CO adsorption on ordered Cu-Pd alloy surfaces and surface alloys has been studied using density functional theory (DFT) within the framework of the generalized gradient approximation (GGA). On the surface alloys, the CO adsorption energy at the top sites decreases with increasing concentration of the more reactive metal Pd. This surprising ligand effect is caused by the effective compressive strain induced by the larger size of the Pd atoms. On the other hand, at the most favorable adsorption sites the CO binding becomes stronger with increasing Pd concentration which is caused by an ensemble effect related to the availability of higher coordinated adsorption sites. At the surfaces of the bulk alloys, the trends in the adsorption energy as a function of the Pd concentration are less clear because of the strong Pd-Cu interaction and the absence of effective strain effects.