Article pubs.acs.org/JPCC
Role of Carbon Support for Subnanometer Gold-Cluster-Catalyzed Disiloxane Synthesis from Hydrosilane and Water Rameswar Bhattacharjee and Ayan Datta* Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur 700032, West Bengal, India S Supporting Information *
ABSTRACT: We studied the mechanism for the formation of disiloxane from hydrosilane precursor using plane-wave density functional theory (DFT). Si−O−Si bond linkage of disiloxane is an essential framework of many useful materials. The reactions are catalyzed by the presence of subnanometer Au cluster on graphitic support. Graphene support lowers the energy barrier of the ratelimiting O−H bond activation of water by ∼4.0−9.0 kcal/mol. The rate-limiting step is shown to be accelerated by the presence of defects in graphene support. Such high activity of Au cluster over carbon support is attributed to the enhanced charge transfer from cluster to the adsorbed substrate in the presence of the support. Regeneration of the catalyst through dehydrogenation of H2 from (H2)Aun···Gn is shown to be facile. the C−H activation by small gold cluster.25 Most preferred supports for gold cluster (Aun) are metal oxides such as TiO2,26 Fe2O3,27 CeO2,28 MgO,29 and Al2O3.30 However, more recently, gold clusters supported on carbon, boron nitride (BN), and silica (SiO2) are also being employed for several reactions.31−35 Carbon-based material has attracted considerable attention as a support of metal nanocluster. Among them, in particular, graphene, a one-atom thick carbon sheet, has been found to be more promising owing to its unusual electronic and mechanical property.36−38 Because of its high specific area, graphene can offer an ideal support for growing and anchoring Au nanoparticles and hence has been exploited in heterogeneous catalysis.39,40 In this regard the contributions of Wilcox and coworkers are noteworthy.41,42 Thermally, a single layer of graphene is stable up to 500 °C in the air, as suggested from Raman spectroscopy.43 However, after 520 °C, defects appear, comprising Stone−Wales, monovacancy, and divacancy defects, among which the divacancy type is thermodynamically more favored and, consequently, more abundant in nature.44 Nevertheless, in the presence of water, some of the dangling bonds at the edge of graphene may induce edge-oxidation, leading to the generation of hydroxylated graphene oxide regions. Metal−embedded graphene has also been experimentally fabricated with high thermal stability.45 By employing DFT, Giovannetti et al. observed that the interaction in metal− graphene can arise due to either chemisorption or physisorption depending on the choice of metal.46 Several studies found that platinum cluster over carbon support is an excellent
1. INTRODUCTION The exceptional activity of metal nanoparticles is one of the fundamental topics in heterogeneous catalysis. In the past decade, gold has received considerable attention in the catalysis community due to its excellent catalytic activity.1−6 A series of factors such as concentration of low coordinated gold atoms, quantum size effects, interaction with underlying support, and existence of cationic and anionic gold are a few vital factors that control the catalytic performance of supported gold particles.7−11 Gold in bulk is known to be chemically inert and therefore regarded as a poor catalyst; however, works led by Haruta and Hutchings expose the great importance gold nanostructures for various kind of industrially important chemical transformation. The well-explored reaction that involves supported gold cluster is CO oxidation by Haruta and is considered as the landmark.12 Besides this, C−C bond formation,13 olefin epoxidation,14,15 alcohol oxidation,4,16 H2O2 synthesis,17 and selective hydrogenation18 are a few that are of particular interest in the chemical industry. Even a highly dispersed gold catalyst is very active for environmental applications like sensing hazardous gas19,20 or removing offensive odors.21 Recently, several reactions that are catalyzed by supported gold nanoparticles have been carried out in water, which therefore offers an environmentally benign alternative to the conventional route that utilizes costly and harmful organic solvent.5,22 In fact, sometimes water plays a crucial role by activating the catalyst.23 In heterogeneous catalysis, the underlying support plays a critical role by enhancing the catalytic performance of the loaded metal cluster. In particular, metal−support interaction (MSI) effects cause unique changes in the structural and electronic property of the combined system, which is absent in the individual material.24 Recently, we have shown that the TiO2 (110) support plays a key role for © 2017 American Chemical Society
Received: May 9, 2017 Revised: July 25, 2017 Published: August 25, 2017 20101
DOI: 10.1021/acs.jpcc.7b04419 J. Phys. Chem. C 2017, 121, 20101−20112
Article
The Journal of Physical Chemistry C
describe the ionic cores.67 In all cases, the wave function and charge density were limited by kinetic energies of 30 and 300 Ry, respectively. The method of Gaussian smearing was used with a smearing width of 0.01 Ry. Brillouin zone integration was carried out with 3 × 3 × 1 k-mesh.68 Dispersion interactions was incorporated by using Grimme’s DFT-D2 empirical formalism.69 The convergence criterion for the ionic relaxation was set such that the total force must be
