Highly Efficient and Selective Photocatalytic Nonoxidative Coupling of Methane to Ethylene over Pd-Zn Synergistic Catalytic Sites

Photocatalytic nonoxidative coupling of CH_(4)to multicarbon(C^(2+))hydrocarbons(e.g.,C,H4)and H,under ambient conditions provides a promising energy-conserving approach for utilization of carbon resource.However,as the methyl intermediates prefer to undergo self-coupling to produce ethane,it is a challenging task to control the selective conversion of CH to higher valueadded CH4.Herein,we adopt a synergistic catalysis strategy by integrating Pd-Zn active sites on visible light-responsive defective WO_(3)nanosheets for synergizing the adsorption,activation,and dehydrogenation processes in CH_(4)to C_(2)H_(4)conversion.Benefiting from the synergy,our model catalyst achieves a remarkable C^(2+)compounds yield of 31.85μmolgh with an exceptionally high C,H4 selectivity of 75.3%and a stoichiometric H_(2)evolution.In situ spectroscopic studies reveal that the Zn sites promote the adsorption and activation of CH_(4)molecules to generate methyl and methoxy intermediates with the assistance of lattice oxygen,while the Pd sites facilitate the dehydrogenation of methoxy to methylene radicals for producing C_(2)H_(4)and suppress overoxidation.This work demonstrates a strategy for designing efficient photocatalysts toward selective coupling of CH_(4)to higher value-added chemicals and highlights the importance of synergistic active sites to the synergy of key steps in catalytic reactions.

Nucleation and Growth Mechanisms for Pd-Pt Bimetallic Nanodendrites and Their Electrocatalytic Properties

In a seed-mediated synthesis, nanocrystal growth is often described by assuming the absence of homogeneous nucleation in the solution. Here we provide new insights into the nucleation and growth mechanisms underlying the formation of bimetallic nanodendrites that are characterized by a dense array of Pt branches anchored to a Pd nanocrystal core. These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K2PtCl4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution. Transmission electron microscopy (TEM) and high-resolution TEM analyses revealed that both homogeneous and heterogeneous nucleation of Pt occurred at the very early stages of the synthesis and the Pt branches grew through oriented attachment of small Pt particles that had been formed via homogeneous nucleation. These new findings contradict the generally accepted mechanism for seeded growth that only involves heterogeneous nucleation and simple growth via atomic addition. We have also investigated the electrocatalytic properties of the Pd-Pt nanodendrites for the oxygen reduction and formic acid oxidation reactions by conducting a comparative study with foam-like Pt nanostructures prepared in the absence of Pd seeds under otherwise identical conditions.

Synthesis and Optical Properties of Cubic Gold Nanoframes

This paper describes a facile method of preparing cubic Au nanoframes with open structures via the galvanic replacement reaction between Ag nanocubes and AuCl_(2)^(-).A mechanistic study of the reaction revealed that the formation of Au nanoframes relies on the diffusion of both Au and Ag atoms.The effect of the edge length and ridge thickness of the nanoframes on the localized surface plasmon resonance peak was explored by a combination of discrete dipole approximation calculations and single nanoparticle spectroscopy.With their hollow and open structures,the Au nanoframes represent a novel class of substrates for applications including surface plasmonics and surface-enhanced Raman scattering.