Preparation Of Ordered Mesoporous CuCo Catalysts And Their Catalytic Performance For Syngas To Low Carbon Alcohols

Low carbon alcohols are widely used as fuel,gasoline additive and chemical intermediates.The lack of petroleum resources hinders the sustainable production of low carbon alcohols,so it is necessary to develop an alternative way to produce low carbon alcohols.Catalytic synthesis of low carbon alcohols from syngas derived from coal,natural gas or renewable biomass is a promising approach.CuCo catalyst is considered to be one of the most active non-noble metal catalysts for the synthesis of low carbon alcohols.Cu is the active site of CO dissociation adsorption and insertion,and Co is the active site of CO dissociation and chain growth.In traditional CuCo catalysts prepared by impregnation method,metal active species tend to aggregate,especially Cu particles tend to aggregate and grow at high temperature,resulting in low catalytic activity and low selectivity of alcohol products.Therefore,improving the dispersity of Cu and Co species and strong synergistic catalysis in CuCo catalyst is the key to improve the selectivity of low carbon alcohols.In order to solve the problem of the dispersion of active sites and the synergy between CuCo catalysts,for CuCo catalyst,different carriers（SiO₂,Al₂O₃,La₂O₃,ZrO₂）can affect the dispersion of active components of the catalyst.On the other hand,the large specific surface area and uniform pore structure of ordered mesoporous structure can improve the dispersion of metal species and reduce the particles of metal species,thus improving the catalytic activity.Based on ordered mesoporous structure,CuCoAl and CuCoZr catalysts with ordered mesoporous structure were obtained by Evaporation-Induced Self-Assembly（EISA）method,which introduced Cu and Co into the mesoporous structure at the same time.Combined with N₂ physical adsorption-desorption,small-angle XRD,in-situ XRD,TEM,H₂-TPR,CO-TPD,XPS and in-situ DRIFT,the effects of different Cu/Co atomic ratios and preparation methods on the structure,surface adsorption state,elemental valence distribution and CuCo interaction of the catalysts were investigated.The structure-activity relationship of the catalyst was also analyzed.The main conclusions are as follows:（1）A series of CuCoAl catalysts with different Cu/Co atomic ratios were prepared by EISA method to study the effect of the synergy between Cu-Co on the hydrogenation of CO to low carbon alcohols.The results showed that the crystal structure,morphology and surface electronic structure of CuCoAl catalyst were not significantly affected by different Cu/Co atomic ratio.Cu and Co elements are evenly distributed in Cu₁Co₁Al catalyst,and the Cu particle size is the minimum after reduction.Cu₁Co₁Al catalyst has a lower H₂ reduction temperature,and the CO desorption amount at high temperature is 1.54 mmol/g.XPS results show that there is strong interaction between CuCo of Cu₁Co₁Al catalyst.The evaluation results show that the Cu/Co atomic ratio significantly affects the catalytic activity of the catalysts,and CuCoAl catalysts with different Cu/Co atomic ratio show better conversion than CuAl and CoAl catalysts.When Cu/Co=1,the catalytic performance is the best,the CO conversion is 32.9%,the total alcohol selectivity is 17.4%,the total alcohol yield is 59.4 mg/（gcat·h）,C₂₊ alcohol yield is 20.5 mg/（gcat·h）.（2）A series of CuCoZr catalysts supported by ZrO₂ were prepared by EISA method,and the content of CuCo metal in the catalyst was up to 40%.The catalytic performance of CuCoZr catalyst was compared with that of CuCoZr-CP catalyst prepared by co-precipitation（CP）method.The results show that all CuCoZr catalysts prepared by EISA method have ordered mesoporous structure,and the specific surface area increases first and then decreases with the increase of Cu/Co atom ratio.The Cu₃Co₁Zr catalyst has the largest specific surface area and CO adsorption capacity,which are 143 m²/g and 0.33 mmol/g,respectively.The Cu grain size of the catalyst was only 9.1 nm,and the CO conversion was 74.9%,the spatiotemporal yield of C₂₊alcohol in total alcohol was 75.2 mg/（gcat·h）,and the molar fraction of ethanol was 31.0%,which were obviously better than CuCoZr-CP catalyst with the same composition.The reaction path on the surface of Cu₃Co₁Zr catalyst was analyzed by in-situ DRIFT,the result showed that a large amount of-OH and bridged CO adsorbed on the surface of Cu₃Co₁Zr catalyst promoted the formation of CHx intermediates,which was conducive to improving the selectivity of C₂₊alcohol.For CuCoZr-CP catalyst,the specific surface area was smaller,and the active metal species were agglomerated after calcination.The Cu species particles were larger after in-situ XRD reduction,and the CO conversion rate was only 31.5%,the selectivity of total alcohol was 15.8%,and the spatial and temporal yield of C₂₊alcohol was only 21.7 mg/（gcat·h）,the molar fraction of ethanol was 28.2%.