Regulating Hydrogenation Selectivity Of Cinnamaldehyde And Carbon Dioxide Based On Noble Metal/Metal Organic Thin Layer

The rapid development of human society and science and technology has led to a sharp rise in the demand of energy and resources,and triggered a series of energy,resource and environmental crises.Developing routes of resource regeneration to meet the demand of social development have become a current research hotspot.The conversion of renewable resources（including the catalytic conversion of abundant biomass and CO₂ on the earth）into high value-added chemicals or fuels is of great significance for solving current energy and environmental problems.Hydrogenation reaction is one of the important reaction in the field of catalysis and has received extensive attention,furthermore,25%processes of chemical conversion involve at least one hydrogenation step.However,biomass hydrogenations are prone to produce various reduced products（hydrogenation of CO₂ andα,β-unsaturated aldehydes with conjugated C=O and C=C bonds）,and processes of products separation require additional cost and energy consumption.Therefore,precise c ontrol of the selectivity of hydrogenation reactions is crucial for the utilization of renewable resources.This thesis focuses on metal-organic layer（MOL）supported noble metal（Pt or Pd）nanocatalysts,controllable preparation of one or two or even three reduction products of cinnamaldehyde were achieved by strategies of CO₂ induced surface modification or dynamic combination of transfer/catalytic hydrogenation;improving the CO₂hydrogenation activity and product selectivity was realized by the strategy of dimensional control of metal-organic framework.The specific contents are as follows:（1）Based on Pt/MOL combined with strategy of CO₂ induced surface modification,the C=O bonds were selectively hydrogenated to realize selective conversion ofα,β-unsaturated aldehydes to corresponding unsaturated alcohols.0.5MPa CO₂ were introduced into Pt/MOL based cinnamaldehyde hydrogenation,the selectivity of cinnamyl alcohol was increased from 65%to 92.7%at 100°C and 1.5MPa H₂ for 1.0 h.Pt/MOL had well catalytic stability,the catalytic activity and selectivity were maintained after six recycle runs.This strategy could extend to hydrogenation of a series ofα,β-unsaturated aldehydes to corresponding unsaturated alcohols.Based on in situ Fourier transform infrared spectroscopy,density functional theory calculations and comparing experiments,the intermediates of HCOO*and HCO₃*were formed on the surface of Pt in Pt/MOL in presence of CO₂,resulting in dominant absorbed-state of cinnamaldehyde shifting from parallel to perpendicular configuration and prior hydrogenation of C=O bonds and promoting of COL selectivity.（2）Based on Pt/MOL combined with strategy of dynamic combination of transfer/catalytic hydrogenation,unsaturated alcohols and saturated alcohols were obtained selectively by exclusive hydrogenation of C=O bonds or complete hydrogenation of C=O and C=C bonds under the mild conditions.Using ammonia borane as hydrogen source,unsaturated alcohols with 100%conversion and selectivity could be exclusively produced through transfer hydrogenation of C=O bonds with ammonia borane.Saturated alcohols could be selectively synthesized by synergistic action of ammonia borane and Pt/MOL,the latter of which simultaneously dehydrogenated ammonia borane and hydrogenated the C=C bonds.The combination of two hydrogenation mechanisms not only could regulate the chemoselectivity of hydrogenation reactions but also avoided the usage of external H₂ source.This strategy could be extended to variousα,β-unsaturated aldehydes hydrogenation,and the catalysts could be recycled for several times without any loss of activity.（3）Based on Pd/MOL combined with strategy of dynamic combination of transfer/catalytic hydrogenation,unsaturated alcohols,saturated aldehydes and saturated alcohols were obtained selectively by exclusive hydrogenation of C=O or C=C bonds or complete hydrogenation of C=O and C=C bonds in water.Impressively,unsaturated alcohols were prepared in 100%conversion and selectivity by the room temperature transfer hydrogenation of cinnamaldehyde with ammonia borane;while a series of saturated aldehydes were obtained with 100%conversion and>90%selectivity at 80°C by the catalytic hydrogenation with in situ H₂ released from ammonia borane and Pd/MOL(Turnover frequency=0.98 s^-1 for cinnamaldehyde).On the other hand,cinnamaldehyde could be readily converted into the saturated alcohol through a combination of transfer and catalytic hydrogenation in one pot.The exclusive hydrogenation of C=O bonds of ammonia borane were associated with the strong interaction between ammonia borane and C=O bonds instead of C=C bonds.Pd/MOL showed very high catalytic activity for hydrogenation ofα,β-unsaturated aldehydes into saturated aldehydes because of the unique porous layered structure and amphipathic nature of MOL.Moreover,this catalytic system had excellent recyclability and universality for variousα,β-unsaturated aldehydes hydrogenation under sustainable conditions avoiding the use of organic solvents and extra high-pressure H₂ source.（4）Based on 1.5 nm ultrathin Pd/Zr-MOL nanosheet combined with strategy of dimensional control of metal-organic framework,high CO₂ hydrogenation activity and CO selectivity in reverse water gas shift reaction were realized.The catalytic performance of CO₂ hydrogenation by fixed bed reactor indicated that Pd/Zr-MOL-Na BH₄ had the highest 19.66%CO₂ conversion and 98%CO selectivity at300°C.After SEM,AFM,TEM,N₂ sorption isotherms and comparing experiments indicated that ultrathin structure was maintained without further aggregation or regrowth only by Na BH₄ reduction,and had well-exposed Pd active sites,the non-porous structure and the smaller BET specific surface area,leading to favorable desorption of CO from Pd/Zr-MOL-Na BH₄.Compared with catalysts of Pd/MOL-25with 25 nm thickness and the three-dimensional Pd/Ui O-67-bpy,Pd nanoparticles were located within the layered or three-dimensional structure,that would increase CO diffusion path and promote CO further hydrogenation to CH ₄.