Preparation And Hydrogen Absorption/Desorption Properties Of Palladium/Alumina Composite

As the most promising clean energy in the 21st century,hydrogen energy is an important part of the future energy system.Hydrogen and its isotopes are widely used in agriculture,industry,medicine,geology,environmental protection and other fields.As a fuel for nuclear fusion reaction,tritium is an important strategic material of the country.Therefore,the development of hydrogen isotope separation technology has strong practical significance.Thermal Cycling Absorption Process(TCAP)is a new semi-continuous gas chromatography separation technology.It adopts the hydrogen isotope effect of palladium as the separation principle and has the advantages of high efficiency,safety and operability.However,Palladium as the separation material has serious pulverization phenomenon.In order to find the hydrogen isotope separation material that can meet the application requirements,the present study employed alumina support to protect palladium from pulverization.X-ray diffraction(XRD),BET surface area measurement,transmission electron microscopy(TEM)observation and other techniques were used to analyze the morphology and structure of the material.Its hydrogen storage properties,hydrogen absorption/desorption cycling performance and the influence of heat treatment on the properties of hydrogen absorption and desorption were studied.The main contents are as follows:In order to ensure the loading effect of palladium,the alumina support was heat treated at different temperatures.The phase analysis and specific surface area measurement of the heat treated alumina were carried out.It was found that the alumina heated at 550～900℃ processed a misconstrue of γ-Al2O3 which was suitable for use as support material with large specific surface area and small pore size.Palladium-loaded alumina composites(Pd/Al2O3)with a palladium content of 40.1wt.%were prepared by impregnation-reduction method using Pd chloride as precursor.XRD analysis showed that the precursor palladium salts were fully reduced and no other impurities were introduced.SEM,TEM and specific surface area analysis showed that palladium nanoparticles were well dispersed in the pores of the Al2O3 support.The composites still had a large specific surface area with a palladium loading amount of 40.1wt.%,indicating that the support could load more palladium.The test results of hydrogen storage performance of Pd/Al2O3 composites show that compared with pure palladium,the saturated hydrogen absorption capacity of the composites decreased slightly.Both the absorption/desorption plateau pressure and plateau slope increased.The absolute values of enthalpy and entropy changes of hydrogen absorption/desorption decreased.The kinetic properties were significantly improved with a hydrogen absorption rate 5 times faster than that of pure palladium.Pd/Al2O3 composites underwent 1000,2000 and 4000 thermally induced hydrogen absorption/desorption cycles.The effective hydrogen absorption,hydrogen absorption/desorption plateau pressure and hydrogen absorption kinetic control mechanism of the samples remained practically unchanged after different cycles,and there was no obvious rupture of Al2O3 support or pulverization of palladium particles.The results show that Pd/Al2O3 composite had stable hydrogen absorption/desorption cycle properties and anti-pulverization properties,which could meet the long-term use requirements of hydrogen isotope separation process.BET measurement on the Pd/Al2O3 composites heat treated at 600～1000℃ was carried out.The results showed that the variation trend of specific surface area and pore size of Pd/Al2O3 composites with temperature was consistent with that of alumina support.The specific surface area and pore volume decreased rapidly upon the changed of the alumina support microstructure,while the average pore size increased sharply.The hydrogen absorption/desorption properties of Pd/Al2O3 composites heat treated at 650,800 and 950℃ were tested.The results show that the hydrogen absorption and desorption plateau pressure of the samples heat treated at 950℃increased obviously by 30%and 80%,respectively.The hydrogen absorption capacity was significantly reduced,which could be attributed to the pore melting or collapsing during the crystal transformation of the alumina support,making it difficult for palladium enclosed in the pores to absorb hydrogen.The kinetic properties of the samples after heat treatment were better than those of the initial samples-the time taken for the samples heat treated at 800 and 950℃ to reach 90%of the total hydrogen absorption capacity was less than 1s.The above results are expected to provide experimental basis for filling materials selection and process optimization of TCAP technique.