Synthesis Of Non-noble Metals (Cu,Ni) Catalysts And Their Catalytic Properties In Hydrogenation Reactions

With the increasing shortage of other traditional non-renewable resources such as coal,oil and natural gas,the energy crisis and environmental pollution problems have become sharply serious,therefore,the development and utilization of renewable clean energy has become increasingly important.As the most abundant organic carbon source,lignocellulosic biomass is considered to be the best substitute for traditional fossil fuel because of its advantages of renewable,abundant in reserves,easy access and environmental friendliness.But the main factor for restricting biomass from directly replacing traditional fossil fuels is that its oxygen content is too high,resulting in its combustion calorific value being too low.However,by designing an efficient catalytic system,potential biofuels and high value-added chemicals can be obtained,which can meet the society's increasing energy needs.Currently,hydrodeoxygenation(HDO)is the most effective way to solve this problem,and the key lies in the construction of HDO catalysts with high activity,specific selectivity and good stability.This dissertation takes vanillin,a typical model compound in lignocellulose,as the main research object,and in view of its technical barriers in the practical application of industrialization,such as the easy loss of catalyst active components,the complicated preparation process,and the poor stability in polar solvents(especially in water),low atom utilization efficiency and harsh catalytic reaction conditions.This dissertation aims to construct a highly active non-noble metal(Cu,Ni)catalyst through a green and simple preparation strategy to achieve the selective hydrogenation of unsaturated aldehydes and ketones under relatively mild conditions,and further reveals the relationship of reaction mechanism,the catalytic mechanism and the structure-effect relationship existing between the catalyst and the catalytic reaction.The main research contents and development work are as follows:1.Activated carbon supported copper catalyst(Cu/AC)and its catalytic performanceUtilizing the reducibility of activated carbon to synthesis highly dispersed Cu/AC catalyst(copper nanoparticles with a particle size of 20-30 nm evenly embedded in activated carbon)by carbothermal reduction method in one step.The typical model compound vanillin was selected for the catalytic performance study of selective HDO.The results showed that when the catalyst was calcined at 600?,its active component was mainly zero-valent copper,and shows the excellent hydrogenation performance for both of vanillin HDO in the aqueous phase and transfer hydrogenation(TH)in organic phase to product 2-methoxy-4-methylphenol in highly selectivity.When the water is used as solvent,under 120?,2.0 MPa H2,5 h reaction conditions,the vanillin can achieve 99.9%conversion through HDO and its MMP selectivity can reach 93.2%;The catalyst can convert 99.8%vanillin to MMP(99.1%)with high selectivity through TH reaction as isopropyl alcohol is used for the solvent and hydrogen donor and under the reaction conditions of 180?,2.0 MPa N2,5 h).The catalyst has good reusability and cycle stability during the TH reaction process,in addition,the catalytic activity and selectivity did not decrease after five catalytic reactions and the active component element Cu did not lose significantly.2.Multifunctional catalytic performance of subnanometric composites constructed by clusters and atomic copperThe highly dispersed Cu/AC catalyst obtained by carbothermal reduction showed a good performance of vanillin hydrogenation,but the Cu nanoparticles in the catalyst were distributed at 20-30nm in size,which limited the hydrogenation activity due to their large size.In order to achieve better atomic-level dispersion of active metals,construct high-energy active interfaces,and significantly improve catalytic efficiency,we prepared a dispersed,high-loaded Cu catalyst(Cu0/Cu-doped SiO2)by ammonia-assisted sacrificial template method,which is a subnanometric composite of clusters and atomic Cu.The synergistic effect of the subnanometric composite formed by the Cu clusters and the atom Cu on multifunctional catalysis is confirmed by DFT calculations and achieved in room temperature hydrogenation,as well as dehydrogenation and transfer hydrogenation under mild conditions.More importantly,the catalyst has good hydrogenation performance to other unsaturated aldehydes and has made some progress in industrial application.This will help to expand the application of subnanometric composite in industrial catalysis.3.Core-shell Cu@C catalyst and its HDO performance in the aqueous phaseMost catalysts have poor stability in water phase systems and the current catalytic reactions are mainly carried out in organic solvents.We constructed a core-shell Cu@C catalyst by reduced pressure distillation.The average particle size of Cu nanoparticles is about 20 nm,the highly dispersed within the hollow carbon cavity and makes each cavity become a hollow carbon micro reaction environment,not only can effectively inhibit the grow up of Cu nanoparticles,improves the catalytic activity,also can reduce the loss of the active component,improve the stability of catalyst in the water phase system.The results showed that the core-shell Cu@C catalyst was more stable in water phase hydrogenation than the traditional carbon-based supported cu-based catalyst,and its catalytic activity did not decrease significantly after five times of repeated use.4.Highly dispersed Ni catalyst and its HDO performance in the aqueous phaseIn order to further improve the atomic utilization efficiency and enhance the intrinsic catalytic activity on the basis of reuses of the catalyst in the aqueous phase system.Therefore,we synthesized a high-dispersed Ni at atomic-level catalyst(HD-Ni/N-CMS)by ultra-high temperature ion exchange method.The catalyst is high dispersed Ni at atomic-level anchored on N-doped carbon molecular sieve.During the whole research process,we ensured that the molar ratio of the Ni content of vanillin and the catalyst was the same,and found that when the Ni content of the catalyst was only 0.56%,the carbonyl group(C=O)in vanillin could still be well activated and converted into MMP by highly selective hydrogenation.The normalized conversion frequency(TOF)to a single Ni site is up to 1041.7h-1,its performance is comparable to that of most noble metal catalysts.Moreover,the stability and reusability of this catalysts are good in the aqueous phase,and it has a good prospect of industrial application.