Size-Dependent Reaction Mechanism For Propane Dehydrogenations By Gold Clusters Catalyzed Au_N~q(N=1-8,q=0,±1):A Density Functional (DFT) Theory Study

Note that the olefin is a primary starting material towards selective synthesis of alcohol, acetaldehyde, isopropanol, carboxylic acids, Propylene cyanide, acetone, butanol and acrylic etc. The steam cracking process is a commonly used method in petroleum geology and chemistry to produce light olefin such as ethylene and propylene, the production capacity can not feed the ever-increasing demand for propylene because of the grow of demand of olefin derivatives. So, Direct dehydrogenation(DDH) by rich resources of propane production is an inexpensive way to increase the production and of great application potentials is an inexpensive in industry.The oxidative dehydrogenation(ODH) and dehydrogenation are two major processes in conversion of olefin from alkane. The selection of catalyst is the key of catalytic dehydrogenation of propane. The traditional experiment screening workload big, cycle is long and cost is high. Calculated using density functional theory can well solve these problems.Due to the unique physicochemical properties of the precious metals nano clusters, nanosized gold clusters have attracted widespread research interests during the past few decades. Feyel et al found that the gas phase VxOy~+ cluster is correlated with the formal valence state of the V atom in the VxOy~+ cluster with a maximum for the high-valent vanadium species, which is in consistence with the tendency in bulk phase of vanadium oxide catalysts. The gas phase experiments has also revealed that the 5d transition metal cations(such as Pt~+, Os~+, and Ta~+) can more readily dehydrogenate methane to the metal-cabene complex through a metal insertion mechanism than the 3d and 4d transition-metal cations. In recent, the subnanometre platinum(Pt) cluster, Pt8-Pt10, were identified highly reactive and selective for the catalytic dehydrogenation of propane, which are about 40 – 100 times more active for the ODH of propane than the VxOy and Pt based catalysts and maintained high selectivity for formation of propylene over the by-products. The highly reactive and selective of Pt8-Pt10 is the cause of the unique affiliate ligand and the quantum effects of nano clusters. However, the study on the catalytic activity of Au cluster towards alkane activation was very limited. The gas phase experiments indicated the gold anion(Au–) weakly interacts with the methane, the neutral gold atom may react with methane to give insertion product via a photolysis process, and the Au~+ is unreactive to methane under thermal conditions. Pure gold cluster cation(Au~+) were found inert toward CH4 under single-collision experimental conditions, while the adsorption of multi-CH4 molecules were observed in the multi-collision conditions. A recent joint temperature-dependent radio-frequency(RF) ion-trap mass-spectrometry measurements and first-principles theoretical calculations revealed that the bare Au2 cation(Au2~+) can selectively activate methane, leading to formation of ethylene and release of H2. The detailed study of binding energies of CH4 to AuN~+(N=2-6) indicated strong size-dependent relationship that the binding energy decreases rapidly with the increase of cluster size.In order to examine catalytic activity of Au cluster toward the dehydrogenation process of propane, the reaction mechanism of propane dehydrogenation has been studied in this thesis. we performed detailed density functional(DF) study on a series of neutral and charged Au clusters. By comparing dehydrogenation activity of propane and propylene selectivity on difference nano-sized Au clusters, Explain the Au clusters catalyst particle size effect.