Fe,Co,Ni And Cu Metallic Nanoparticles For Hydrogen Generation From Al-ethanol Reaction

The consumption of fossil fuels and the aggravation of environmental pollution problems are constantly threatening the life of human societies,which urgently requires the researchers to develop the carbon-emission-free and renewable alternative energy sources.Hydrogen is considered as one of the most promising new energy sources to replace fossil fuels due to its clean and sustainable characteristics.Nevertheless,storage and transportation of hydrogen are the biggest obstacle for its widespread use.Among various hydrogen production strategies,the Al-H₂O reaction for hydrogen production is a facile way for in-situ hydrogen generation,however,Al is easily to be oxidized and thus hindering the reaction between Al and H₂O,and the by-product Al（OH）₃ is of commercially low-value.Compared to H₂O,the reductive ethanol can alleviate the oxidation of Al in the reaction process,and the co-product aluminum ethoxides is an expensive chemical reagent.At present,the studies on the hydrogen generation from Al-ethanol reaction are very rare,and it is necessary to develop more efficient approaches to advance the commercialization of the process.On this base,from the perspective of facile,immediate and controllable hydrogen generation from Al-ethanol reaction,this thesis prepared Fe,Co,Ni,Cu and NiCu nanoparticle（NP）catalysts via the in-situ replacement reaction between Al and metallic ions by using different chlorides as catalyst precursors and/or activating agent.Also,the hydrogen production performance and Al-ethanol reaction mechanism were investigated.The results of the study showed that:（1）Using transition metal chlorides NiCl₂,CoCl₂,CuCl₂ and FeCl₃ as catalyst precursors,in the process of Al-ethanol reaction,Cl^-ions can erode the oxide layer on the surface of Al powder and expose the active Al substrate,which contribute to the release of hydrogen.Ni（2.9 nm）,Co（3.5 nm）,Cu（3.5 nm）and Fe（3.6 nm）metal NPs can be in-situ generated via galvanic replacement reaction between exposed fresh Al and Ni²⁺,Co²⁺,Cu²⁺and Fe³⁺metal precursor ions.Electron transfer interaction effect exists between the in-situ generated metal NPs and ethanol molecules/Al substrates,which is beneficial to promote the adsorption and activation of ethanol molecules,finally accelerating the release of hydrogen.The NiNPs demonstrate a superior catalytic ability with the hydrogen production rate as high as 109 m L-H₂·min^-1·g-Al^-1,and the apparent activation energy of Al-ethanol reaction is 26.94 k J·mol^-1,but the actual hydrogen generation yield is 65%.（2）To solve the problems of low hydrogen yield and high Niconsumption,the AlCl₃and NiCl₂ were respectively used as the activating agent and catalyst precursor.The utilization of Al powder in Al-ethanol reaction is improved through the catalysis of NiNPs and the synergistic effect of AlCl₃.Under the reaction condition,the in-situ generated NiNPs with average particle size of 2.7 nm are homogeneously dispersed.The actual hydrogen yield of the Al-ethanol reaction can reach 96%with hydrogen generation rate of 76 m L-H₂-min^-1-g-Al^-1at the Niloading of 10 wt.%and water bath temperature of 50℃.In addition,the high value-added aluminum ethoxides gels and the supported Ni/Al₂O₃ catalyst can be respectively obtained via the sufficient reflux of Al-ethanol reacted solid residue followed by freeze-drying.（3）To simultaneously realize a higher hydrogen yield,a faster reaction rate and lower cost of the catalyst for Al-ethanol reaction,AlCl₃ and NiCl₂/CuCl₂ were respectively regarded as the promoter and catalyst precursors.The synergistic effect of AlCl₃ and in-situ generated NiCu bimetallic NPs accelerated the Al-ethanol reactions.The particle size of in-situ generated bimetallic NiCu NPs is about 3.1 nm,and the addition of Cu effectively prevents the oxidation and agglomeration of Ni⁰ in NiCu bimetallic NPs.The hydrogen generation rate of the Al-ethanol reaction is 85 m L-H₂-min^-1-g-Al^-1,which is respectively 1.1 and 3.4 times higher than that of the monometallic Niand Cu NP catalysts,and the actual hydrogen yield is also improved to 97%.Furthermore,after freeze-drying of the solid product of the Al-ethanol reaction,NiCu/Al₂O₃ catalyst is obtained and shows respectively 1-fold and 7-fold improvement in ethylene selectivity for acetylene selective semi-hydrogenation reaction compared to monometallic Ni/Al₂O₃ and Cu/Al₂O₃ catalysts.