Regulation Of The Active Sites Of Nickel Cobalt Copper Based Catalysts And Their Effects On The Hydrogenation Of Biomass Derivatives Such As Furfural

The search for renewable green energy is not only for the survival and development of human beings,but also for the survival of all living things on earth.With the introduction of"carbon neutral"strategy,biomass as the only renewable carbon source has attracted a lot of attention in the research of converting it into high value-added compounds.Furan derivatives are the bridge between biomass and alternative carbon source chemicals,and it is important to develop cost-effective and applicable catalysts to catalyze the conversion of furan derivatives.In this thesis,a series of inexpensive non-precious metal-based catalysts were synthesized by a simple method around the conversion of furan-like biomass platform molecules to high value-added chemicals,and the effects of catalyst surface hydrogenation sites and acidic sites on catalyst activity were investigated,and possible reaction mechanisms were proposed accordingly.The main contents are as follows.1.In this study,the modification of Ni/Si O₂ catalyst with Ni SO₄ was used to tailor the hydrogenation activity of the catalyst.The introduction of sulfur species from reduction of Ni SO₄ was expected tackle the excessive hydrogenation of furan ring in FA,aiming to achieve conversion of FA to CPO via ring opening route.The impacts of introduction of sulfur species on catalytic activity/stability was investigated while the reaction intermediates formed in hydrogenation of FA was characterized with in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy（DRIFTS）technique.The results showed that introduction of Ni SO₄ to surface of the Ni/Si O₂ catalyst formed Ni₃S₂ via the reaction between Ni_xS_y generated from the reduction of Ni SO₄and the metallic Ni species.This effectively hinders hydrogenation of furan ring in FA,shifting the major product from THFA to CPO.Formation of Ni₃S₂ reduced capability of the catalyst for hydrogenation of C=C bonds,even with the presence of a small amount of sulfur on surface of the catalyst.Nevertheless,the enhanced abundance of acidic sites with the introduction of Ni SO₄ could catalyze the polymerization of FA and/or its derived intermediates.The acidic sites,however,facilitated hydrogenolysis reactions in hydrogenation of vanillin.The in-situ DRIFTS characterization of hydrogenation of FA over Ni S₁₀/Si O₂catalyst indicated strong adsorption of the C-O-C and-OH functionalities in FA or derived intermediates,facilitating the ring-opening of furan ring to form CPO but not saturation of the ring structures to form THFA.2.In this study,H-ZSM-5 acidic zeolite molecular sieve was used as a carrier to tailor the hydrogenation activity and acid catalytic ability of the catalyst by loading different ratios of bimetallic Co and Cu on it.The loading of Cu particles was designed to weaken the hydrogenation ability of Co metal sites on C=O and C=C for the inhibition of by-product formation and highly selective preparation of cyclopentanone.The reasons for the advantages of the Co_xCu_y/H-ZSM-5 bimetallic catalyst over the monometallic catalyst in terms of selectivity and stability were investigated,while the variations of the adsorbed functional groups on the catalyst surface during FA hydrogenation were characterized by in-situ diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS）technique to study the process changes and reaction mechanism.The results showed that the introduction of Cu effectively regulated the exposure of Co metal sites and inhibited the further conversion of CPO;the distribution of Cu particles on the catalyst surface played a role in stabilizing the metal Co active sites and improved the stability of the catalyst;compared with the monometallic catalyst,the total acidic site area of the Cox Cuy/H-ZSM-5 bimetallic catalyst was slightly decreased,which weakened the polymerization of FA or its derived intermediates.At 170°C,81.8%yield of cyclopentanone could be achieved with a catalyst dosage of 5 mg.The in-situ DRIFTS characterization of FA hydrogenation over Cox Cuy/H-ZSM-5 catalyst showed that the incorporation of a small amount of Cu also promoted the adsorption of oxygen-containing functional groups（C-O-C,-OH and C-O）in FA by the bimetallic catalyst,which facilitated the rearrangement of the furan ring and made it possible to complete the catalytic conversion in a shorter reaction time;the strong adsorption of C=O by the Co-based catalyst reduced the cyclopentanone yield of cyclopentanone.3.In the present study,bio-oil produced by laboratory rapid pyrolysis of biomass was used as the carbon fraction required for the reduction of Ni-based catalysts using silica as a carrier,and the effect of the biomass carbon source on the reduction of the catalyst was investigated.The results showed that the bio-oil carbon source,while acting as a catalyst reduction instead of H₂,also played a role in regulating the dispersion of active sites and the number of metal sites on the Ni-m/Si O₂ catalyst.The size of metal particles on the catalyst became significantly smaller with the increase of bio-oil addition,indicating that the reduction of catalyst by bio-oil carbon source could inhibit the aggregation of metal sites on the catalyst surface and improve the dispersion of metal sites on the catalyst surface.Excessive bio-oil,on the other hand,formed carbon accumulation on the catalyst surface and encapsulated the metal sites,thus regulating the number of active sites and causing changes in furfural hydrogenation activity and product selectivity.