Theoretical Studies On The Interaction Of Palladium-based And Platinum-based Clusters With Small Molecules

Renewable energy and clean energy resources and the development of environmentally friendly and practical systems are important assurance for economic development,national security and people’s healthy life.Hydrogen has attracted much attention because of its light weight,high calorific value and non-polluting water after combustion.Conventional hydrogen production is generated from fossil fuels,especially natural gas.In the process of hydrogen production,the non-singularity of the reaction and the diversity of products lead to high energy consumption,low output,and abundant products,resulting in a complicated separation process,etc.,in addition,fossil fuels are mainly composed of alkanes and by-products of carbon oxides can cause environmental problems,these have become obstacles to the development of hydrogen production,while use of catalysts to catalyze water splitting to produce hydrogen can reduce the energy required for water splitting and without pollution to the environment,which is an efficient and energy-saving method.It has been found that most of catalytic reactions occur on the surface,and nano-scale clusters are considered as catalysts due to their novel physicochemical properties and large surface-to-body ratios that are different from macroscopic substances.In the study of the law of size evolution and property change of clusters,as well as the characteristic law of interaction between clusters and the outside world,a strong correlation between properties and size was found.As a result,when studying the microstructural characteristics and property evolution of clusters,it was found that clusters of certain structures can also be used as catalysts for some reactions.Pd and Pt have been proven to be one of the most efficient catalysts for hydrogen production,but their limited resources and high cost hinder their large-scale applications.Compared with bulk materials,nanomaterials have more efficient catalytic performance and more active sites.The emergence of Pd and Pt cluster catalysts opens a new avenue to solve this dilemma.Considering the current trial-and-error situation in developing efficient catalysts,which involves a lot of wasted time and cost,rapid screening/design of efficient cluster catalysts is crucial and much needed,and advanced computer-aided design processes can help in the search for a reusable and efficient catalyst and understanding of its internal mechanisms.The first-principles calculations based on density functional theory with the powerful computing power of the computers,it is used to analyze and find excellent cluster catalysts for dissociating water molecules,the active sites are inherent properties of the material,which can be easily obtained by optimizing its initial structure without considering other complicated processes.This can greatly reduce the computational cost.Nanoclusters composed of metal atoms,such as Al,Fe,Pd and Pt clusters,have been shown to be highly reactive and can be used as catalysts for hydrogen generation from water splitting.However,catalyst "poisoning" has always prevented its wider and deeper application in the energy industry.One of the more effective and promising ways to improve catalyst "poisoning" is to alloy the precious metals with abundant elemental atoms.The electronic structure,active sites of adsorbed water molecules,and the intrinsic reaction coordinates of water splitting on clusters with "image number" characteristics are theoretically investigated by density functional theory based on first principles,using Pd and Pt clusters as the objects.The reuse of clusters after dissociation of water molecules,such as re-dissociation of water molecules,adsorption,and identification of small molecular gases,and catalyst"reactivated" by oxidation of CO.It is expected that the research results will provide some theoretical help for the design and application of nanoclusters as a new generation of catalysts.The content and the obtained research results are as follows:(1)Maximizing the performance of the Pd13 cluster to catalyze water splitting for hydrogen production.It can dissociate three H2O molecules one after another to generate three H2 molecules.The intrinsic reaction coordinates of the water splitting reaction on the potential energy surface confirm the path of the reaction.It was found that both Pd13 and its hydrogenproducing products O+Pdi3 and 2O+Pd13 can adsorb water molecules and activate them to dissociate to produce hydrogen.Eventually,it was found that the oxygen-loaded cluster 3O+Pd13 could no longer continue the catalytic dissociation of water for hydrogen production.In addition,it is gratifying that the cluster O+Pd13 can simultaneously adsorb two H2O molecules and decompose them one by one.These findings support that the clusters Pd13,O+Pd13,and 2O+Pd13 are all candidates as promising catalyst materials to catalyze the decomposition of H2O to H2.(2)The sensitivity of adsorption of five colorless and odorless gases,H2,O2,N2,NO,and CO,on the product cluster O+Pd13 after hydrogen production by water decomposition studied in the previous section was investigated.The results show that the deformation energy,bond length,and bond order of the clusters after adsorbing O2,N2,H2,NO,CO explain the stability properties of clusters after adsorption of gas molecules.The global reactivity index,charge transfer,orbital occupancy in the DFT concept and the shift of the Fermi level in the density of states of electrons confirmed that the electronic properties of the clusters O+Pd13 changed differently after adsorbing different gases.Finally,molecular dynamics simulations found that only some of the H2 molecules could be released from the clusters when the temperature was T=3 73 K.The above results confirm that the changes in the structure and electronic properties of the clusters after adsorption of these small molecules are different.The content of this chapter can provide some theoretical help for the design of multi-resolution nanoscale gas sensing devices.(3)The catalytic performance of the platinum clusters in the catalytic water splitting for hydrogen production after the introduction of carbon group elements has been greatly improved.It is confirmed that Pt6X(X=C,Si,Ge)clusters are superior to pure Pt7 clusters and can directly catalyze the dissociation of H2O to generate free H2 molecule and O+Pt6X complexes.In addition,O+Pt6X finally eliminates the problem of catalyst"poisoning" by trapping a CO molecule and then reducing it to a Pt6X cluster.Our results show that the introduction of carbon group elements can effectively enhance the charge-accepting ability of the clusters and evoke active sites,thereby enhancing the ability of Pt6X clusters to extract hydrogen from H2O molecules.This provides theoretical insights into carbon group elements for tuning the properties of platinum nanoclusters.(4)Reducing catalyst size for improving catalytic efficiency is an effective way to develop cost-effective catalysts.Small clusters have attracted attention due to their large specific surface area and high catalytic efficiency.Pt3X(X=Al,Si,Cu)small clusters with a "magic number"structure can be used as catalysts for CO oxidation after catalyzing water splitting for hydrogen production,and the clusters return to the original structure and can be used again as a catalyst for water splitting.This can effectively avoid the phenomenon of "deactivation" after the catalyst is contaminated.Besides,we also found that H2O@Pt3X small clusters have a high absorption coefficient in the visible light region,the use of solar energy can be considered to provide the activation energy for hydrogen production from water dissociation.It is hoped that the results of this study will provide some degree of assistance in designing small clusters for reactions in catalysis.