The Research On Preparation Of Modified Support Palladium-Based Catalyst And Its Catalytic Performance For Hydrogenation Of Carbon Dioxide To Formic Acid

In the past few decades,due to environmental problems such as energy shortages and the greenhouse effect,the development of new materials and new technologies for carbon dioxide capture,storage and utilization has received widespread attention.Using hydrogen energy through fuel cells is one of the promising alternatives to carbon-based fuels in current power generation.The key to achieving a hydrogen economy is to develop a reliable hydrogen storage system that stores large amounts of hydrogen in a safe manner.As a liquid storage form of hydrogen energy,formic acid and formate can be generated by hydrogenation of carbon dioxide,carbonate or bicarbonate in the presence of an effective catalyst,which constitutes a simple and promising carbon neutralization cycle.The research in this paper is mainly aimed at palladium-based heterogeneous catalysis,through carrier-related modification work to achieve efficient conversion of CO₂ to formic acid and formate,to achieve effective use of CO₂ and storage of hydrogen energy.The main work and results of the paper are:1.Using urea and terephthalaldehyde as precursors,we successfully synthesized Pd nanocluster active centers supported on Schiff base modified graphite carbonitride(u-CN₁₀₀)by impregnation.The obtained sheet material showed high catalytic activity,with a conversion frequency（TOF）of 98.9 h^-1,and had good stability in CO₂ hydrogenation.Various influencing factors in the reaction process were studied,including the amount of TPAL added,reaction pressure,reaction temperature,etc.A large number of characterization methods are used to study the structure-activity relationship of the catalyst,including TEM,XRD,XPS,FTIR,HRTEM,EDS and BET.The results show that the high activity and stability of the catalyst are due to the electronic modification of the active component Pd surface,the high dispersion of the precious metal nanoclusters and the strong metal-support interaction.Scattered Schiff base sites and various nitrogen-containing groups are of great significance in the efficient and durable CO₂ hydrogenation system.The catalytic system organically combines carbon-nitrogen materials,Schiff base sites and CO₂ catalytic hydrogenation to formic acid in order to better exert the economic and social value of CO₂.2.We used a high-porosity structure regular phenolic resin as a carrier and hexamethylenetetramine as a curing agent to synthesize a heterogeneous mesoporous Pd-based catalyst by impregnation.The effects of curing agent crosslinking foaming and chloromethyl functionalization,phenol formaldehyde molar ratio（F/P）,CO₂/H₂ reaction pressure,reaction temperature and catalyst stability test were also discussed.The optimized conditions are a reaction pressure of 10 MPa,a reaction temperature of 383.15 K,a reaction time of 2 h and an F/P value of 1:1,which helps to increase the catalytic activity to a conversion frequency（TOF）of 115.9 h^-1.It is worth noting that in the presence of the curing agent hexamethylenetetramine,the mesoporous phenolic resin polymer greatly increased the TOF value,from 90 h^-1 to 115.9 h^-1.Appropriate amount of HMTA added to MPF played a role in foaming and cross-linking curing.These products and intermediates provided and led to surface fluffing,high dispersibility of palladium nanoclusters and increased specific surface area and pore volume of the material as well as firm formation Metal-carrier bond.This discovery provides a promising way for the direct hydrogenation of CO₂,and may have some important significance in the fields of CO₂ conversion and precious metal catalytic chemistry.