Fibers Supported Palladium Oxide Catalyze Hydrogen Production From Formate And Tandem Degradation Of Organic Pollutants

Strong dependence on fossil fuels has made its reserves projected depletion on earth,and the rapid increase of air pollution and global warming.Hydrogen(H₂)is likely to play an important role in the energy portfolio of the future by virtue of its high energy efficiency and environmental friendliness compared with fossil fuels.Formic acid(FA)and its derivatives are well known potential hydrogen-storage material,while the low efficiency and poor selectivity of catalytic hydrogen production limit its development and utilization.In addition,in the fields of the textile printing degradation and dyeing wastewater,it is urgent to develop new technologies to replace the traditional degradation technologies(such as biological,Fenton or photoelectric catalysis)that have the problems of harsh treatment conditions,low efficiency or secondary pollution.In this thesis,titanate nanofibers with high specific surface area and abundant mass transfer channels are used as the support for palladium oxide nanocatalyst,which greatly improves the activity and selectivity of palladium oxide catalyzing hydrogen production from formate at room temperature.Secondly,the abundant active free radicals produced in the process of formate hydrogen production are used as oxidants/reductants for the degradation of organic pollutants including nitrophenols and dyes,and the tandem catalysis system has been successfully constructed.Finally,based on the textile engineering technology,a flexible organic fiber-supported inorganic nano-catalyst system are developed to further improves the activity and stability of the nanocatalyst.This work effectively solves the problem of the agglomeration,deactivation,and ineffective recovery of inorganic nanocatalysts in the real catalytic process,and provides a new idea and method for hydrogen energy development and pollutant treatment.The thesis includes the following three aspects:(1)High-quality crystalline Pd O nanoparticles with Kirkendall nanovoids uniformly supported on titanate nanotubes(kv-Pd O/Ti NFs)are shown to be robust catalysts toward low temperature sodium formate(SF)reforming into CO_x-free H₂without any additives.The maximum H₂ evolution reaction rate can reach 15.8 mol g^-_Pd¹ h^-1,and the corresponding initial turnover frequency(TOF)is as high as 6312.7 h^-1.More importantly,the product of CO_x-free H₂reduces greenhouse gas emissions while avoiding catalyst poisoning and deactivation,making the catalyst highly stable.Based on DFT calculations and experimental observations,the surface Pd sites and terminated oxygen atoms strongly enhance the reactivity of Pd O(101)toward C-H bond as well as water activation,change in the rate determining steps and the reduction of activation energy within the same reaction pathway,which is the fundamental reason of kv-Pd O/Ti NFs efficiently catalyzing SF to produce hydrogen.(2)Pd O_x/Ti NTs(1<x<2)are prepared by the in situ reduction method and subsequent annealing in an oxygen atmosphere,and show high selectivity and catalytic activity for the tandem dehydrogenation of SF and hydrogenation of p-nitrophenol(PNP)to p-aminophenol(PAm P)under mild conditions.Notably,the conjugation effect of PNP make it selectively adsorbed on the O atoms in the Pd O_x species and reduced to amino by the adjacent H radical,and then desorbed from the surface of the catalyst.Therefore,this unique Pd O_x/Ti NTs catalyst shows?100%selectivity and a fast reaction rate,and the rate-limiting step is the reduction of the-NO₂ to-NO.Additionally,after PNP is completely reduced to PAm P,the remaining formate will continue to generate H₂ over Pd O_x/Ti NTs catalyst,and thus the hydrogen utilization rate of the reaction system can reach 100%.(3)Polyimide(PI)fiber is properly etched by surface hydrothermal and combined with palladium oxide nanocatalyst to obtain flexible composite fiber catalytic material,which can solve the problem of agglomeration and deactivation of nanocatalyst.The fiber support provides adsorption sites for the nanocatalytic material and enrich the reaction substrate,establish a micro-environment for the catalytic reaction.Combining the composite fiber catalytic material with the formate hydrogen production reaction for the tandem degradation of azo dyes exhibit an efficient decolorization and degradation effect on a single dye or multiple dyes,which provides a new solution for the treatment of textile printing and dyeing wastewater.