Controllable Preparation Of Pd Nanoparticles On SiO₂ And Application In Catalytic Methane Combustion

The reasonable development and effective utilization of natural gas,clean energy is the guarantee of sustainable development and an important way to achieve green energy-using.Methane is the main component of natural gas,the low-temperature activation of its C-H bonds has always been a hot topic in the field of catalytic chemistry.It is of great practical significance to develop a catalyst,which has high catalytic activity for low-temperature catalytic combustion of methane.This article aims to prepare a series of supported Pd-based catalysts（Pd/SiO₂）with different size distributions by using WI（wet impregnation）,SEA（strong electrostatic adsorption）,DI（dry impregnation）,and CEDI（charge enhanced dry impregnation）methods.The SEA method and CEDI method can obtain highly dispersed,small-sized supported catalysts due to the interaction between the charges,to realize the efficient utilization of noble metals in the catalytic combustion of methane.The main materials involved in this article are the SiO₂ carrier and the Pd-based active site precursor（Pd（NH₃）₄Cl₂）.Through detailed characterization methods,we try to explore the relationship between the active site size,the redox state,and various parameters of the methane catalytic combustion reaction.The main research results are as follows:（1）The SEA method and CEDI method can deprotonate the carrier by OH^-in an alkaline environment,and strong electrostatic interaction is formed between the deprotonated carrier and the positively charged metal precursor ion.The Pd/SiO₂ catalyst has higher Pd dispersion and smaller Pd active site size（compared to traditional impregnation methods:WI,DI,etc.）,which greatly improves the utilization efficiency of Pd.After characterization,we find that the Pd/SiO₂ catalysts which have high dispersion and small size Pd active site morphology have better methane catalytic combustion performance.（2）The surface loading（SL）of the SEA method and the selection of pH regulators will affect the morphology of the Pd/SiO₂ catalyst and the catalytic combustion reaction of methane.If the SL value is too small,most of the carrier will be dissolved（37%）,making the actual loading increase.And the effect of controlling the size of Pd particles becomes weaker.When Na OH is used as a regulator,the introduction of Na⁺will seriously affect the activity of Pd nanoparticles in the catalytic combustion of methane.（3）As the Pd dispersion in the Pd/SiO₂ catalyst increases from 54%to 100%,the TOF decreases accordingly.Besides,the reaction of the Pd/SiO₂ catalyst activity is significantly improved,and the TOF also increases with the increase of the Pd⁰%content（from 74%to81%）.It shows that the catalytic combustion performance of methane of the supported catalyst is related to the oxidation or reduction state of Pd nanoparticles.