Aerobic Toluene Oxidation Catalyzed by Subnano Metal Particles

Abstract

Subnanocatalysts (SNCs) containing various noble metals (Cu, Ru, Rh, Pd, or Pt) with sizes of approximately 1nmw ere synthesized using dendritic poly(phenylazomethine)s as amacromolecular template.These materials exhibit high catalytic performance during toluene oxidation without the use of harmful solvents or explosive oxidants,r esulting in the formation of valuable organic products,including benzoic acid as the major product. In particular,P t 19 SNC with an arrowp article size distribution exhibits extraordinary catalytic activity,w ith at urnover frequency of 3238 atom À1 h À1 ,whichis1700 times greater than that obtained by commercial Pt/C catalysts.Catalytic oxidation of hydrocarbons is acritically important process that converts raw materials into versatile organic compounds. [1] However, the majority of the practices currently employed in industry suffer from several disadvantages,s uch as the use of oxidants hazardous to the environment, poor selectivity,a nd excessive waste generation. Applying molecular oxygen as the oxidant in conjunction with solvent-free reaction systems has attracted considerable attention as ab enign, inexpensive approach to catalytic oxidations. [2] Fort his reason, many researchers have studied nanometer-sized heterogeneous catalysts.H owever,d ecreasing the size of the catalyst to the subnanometer scale would further reduce the quantities of noble metals required for catalysis.The catalytic properties of subnanocatalysts (SNCs) with sizes of approximately 1nmh ave been investigated because the lattice structure normally found in nanoparticles is collapsed in such materials and they exhibit quantum size effects as ar esult of the amorphous surface areas and the irregular electron distributions. [3] Additionally,n oble metal SNCs are resistant to oxidation even under an oxygen atmosphere.A sane xample,n oble metal SNCs composed of Rh, [4] Pd, [5] Pt, [6] and Au [7] exhibit highly effective and selective catalysis during CO oxidation. Size-specific Pt SNCs were also found to be more active for the dehydrogenation of propane than larger nanocatalysts. [8] However,t he precise synthesis of such particles while controlling the quantity of metallic atoms per particle is remarkably difficult.Thedendrimer-templated method is an effective strategy for the synthesis of size-controlled subnano metal particles in conjunction with low polydispersity. [9] Dendrimers provide internal nanospaces that could be suitable for catalytic conversion in the presence of metal particles. [10] Our group has prepared subnano platinum particles with atomic-level precision using fourth-generation dendritic poly(phenylazomethine) species having atetraphenylmethane core (DPAG4-TPM) or amono(2-pyridyl)-triphenylmethane core (DPAG4-PyTPM). [11] Ap rior electrochemical study found that SNCs containing between 12 and 20 Pt atoms exhibit superior catalytic performance. [12] In other work, multi-metal alloy nanocatalysts containing Au,P t, and Cu atoms showed enhanced catalytic activity during solvent-free aerobic...

New Horizon of Nanoparticle and Cluster Catalysis with Dendrimers

“…These results suggest that the catalytic performance of these materials is related to the oxophilicity of the corresponding subnanosized metal particles as determined by the XPS analysis. 160 Size-controlled tin oxide clusters loaded into mesoporous silica possessed CO oxidation activity, which increased with decreasing tin oxide cluster size (Figure 34). 161 The synthesized clusters contained not only stable Sn(IV) but also metastable divalent Sn(II) species.…”

Compatibility between Activity and Selectivity in Catalytic Oxidation of Benzyl Alcohol with Au–Pd Nanoparticles through Redox Switching of SnOx

“…16 These results pointed out to the need to find another route to reduce the surface inert PdO layers on Au-Pd NP catalyst. Pd has a relative high electron negativity and a low oxygen affinity, [17][18] while Sn is considered as an oxophilic metal. 17,[19][20] Thus, this reminds us to consider the possibility of applying tin as a potential promoter for in-situ autogenous reduction of surface PdO layer instead of high temperature H 2 reduction.…”

Synthesis of Asymmetric One-Dimensional Pd on Au Bimetallic Nanostructures

“…The unique properties of metal nanoparticles, which are governed by their shape and size, make them applicable in nanotechnology, optics, − sensing, − surface-enhanced Raman spectroscopy (SERS), ,, biology, ,,, and catalysis. − In that respect, gold and silver nanoparticles − are interesting due to their optical properties, and palladium and platinum nanoparticles have also gained significant attention due to their catalytic activity. , Well-dispersed supported Pt and Pd nanoparticles were found to have excellent catalytic performance. ,− In addition, well-defined one-dimensional (1D) nanostructures composed of a AuNR core and a Pd or Pt shell are of significant interest because they can be utilized as surface plasmon resonance-enhanced catalysts. , Over the past two decades, significant research studies have been reported on mono- and bimetallic nanostructures. − Most of the reported methods for the synthesis of 1D bimetallic nanostructures are based on single crystalline gold nanorods (AuNRs) of aspect ratio (AR) 3 ± 1 as the core, and a metal (M) (M = Ag, Pd, Pt) shell grown around them by chemical and electrochemical deposition methods. ,,,,− Single crystalline AuNRs synthesized by a silver-assisted seed-mediated method have truncated octahedral morphology with (100) and (110) crystal planes at sides and tips, respectively. − Depending on the nature of M deposited, single and polycrystalline<...…”