Construction Of 2D Mesoporous Au/CeO₂/Graphene Composite Nanocatalysts And Their Catalytic Performance For Glycerol Oxidation

In recent years,due to the increasing energy shortage caused by the excessive consumption of traditional fossil energy,biomass resources have received more and more attentions.Compared with traditional fossil fuels,biomass diesel is highly favored because of its unique advantages such as cleanliness,friendliness to environment and regeneration in a very short-term.However,the large-scale industrial production of biomass fuels is inevitably accompanied by the generation of a large amount of glycerol.The large accumulation of glycerol is bound to cause waste of resources and even bring more serious environmental problems.Glycerol is an important basic material in the chemical industry.It can be converted into products with better market value,thereby,helping improve the efficiency of energy.The main conversion pathways include selective oxidation,selective hydrogenolysis,selective dehydration,thermal reduction to syngas,selective etherification and selective transesterification etc.Among these conversion pathways,glycerol selective oxidation has significant research and practical values.In this paper,Au nanoparticles were selected as main active species for catalyzing glycerol selective oxidation.Novel two-dimensional?2D?layered mesoporous cerium oxide/graphene?2D-mCeO₂/G??CeO₂?catalysts were fabricated using two-dimensional layered graphene as a support and KIT-6 as a mesoporous template.Afterwards,Au nanoparticles were loaded onto2D-mCeO₂/G supports via a sol-impregnation method to generate unique Au/2D-mCeO₂/G catalysts.The catalytic performance of Au/2D-mCeO₂/G catalysts for glycerol selective oxidation was systematically studied.The main research contents of Thesis are described as follows:?1?A spherical CeO₂?S-CeO₂?support was synthesized via a hydrothermal method using cerium nitrate as a precursor and ethyleneglycol as solvent.Then,the S-CeO₂ was subjected to the post-treatment of NaOH soaking,high temperature calcination in the presence of H₂,and HF etching to obtain different S-CeO₂?NaOH?,S-CeO₂?H₂?and S-CeO₂?HF?with various surface states.Subsequently,uniform dispersed Au nanoparticles were loaded onto the surface of various S-CeO₂supports via a sol-impregnation method to achieve Au/S-CeO₂?NaOH?,Au/S-CeO₂?H₂?and Au/S-CeO₂?HF?catalysts.Furthermore,the composition,structure,size,morphology and surface property were characterized by means of XRD,SEM,TEM and XPS etc.Finally,the catalytic performance of glycerol selective oxidation on various Au/S-CeO₂ catalysts was systematically investigated and the effects of various catalysts on the glycerol conversion rate and the product selectivity were revealed.It was found that the catalytic performance of Au/S-CeO₂?HF?catalyst showed the highest glycerol conversion rate of 56%after 12 h catalytic reaction.?2?To further optimizing the catalytic performance,a novel 2D-mCeO₂ support synthesized via in-situ forming mesoporous KIT-6 template on 2D graphene nanosheets following the filling of cerium salt precursor into mesoporosities of KIT-6 template.After removing the KIT-6 template via calcination and HF etching and depositing Au nanoparticles via a sol-impregnation method,a2D-mAu/CeO₂/G catalyst with a mesoporous structure and hybridized by 2D layered graphene was obtained.With this method,the 2D-mAu/CeO₂/G catalyst well replicated the highly order mesoporous structure of KIT-6 template while hybridized graphene provided an overall effect of active support,excellent conductivity and synergistic catalysis.As a result,the 2D-mAu/CeO₂/G catalyst exhibited an enhanced catalytic performance for catalyzing the glycerol selective oxidation reaction.It was revealed that the catalytic performance of 2D-mAu/CeO₂/G catalyst showed the highest glycerol conversion rate of 65%after 12 h catalytic reaction with a high selectivity to lactic acid and glyceric acid up to 95%.?3?In order to further investigate the catalytic mechanism,three kinds of comparative catalysts of Au/KIT-6/G,Au/p-CeO₂ and Au/2D-mCeO₂ were prepeared using KIT-6/G,p-CeO₂?powder?and 2D-mCeO₂ as supports following with the deposition of Au nanoparticles via a sol-impregnation method.It was revealed that the ultrafine CeO₂ nanoparitcles formed due to the confinement of KIT-6the loading content of Au nanoparticles and the synergestic interaction among Au,Ce and graphene have significant impacts on the improvement of the catalytic performance of glycerol selective oxidation.