Synthesis And Hydrogen Storage Of Metal-Phosphate Molecular Sieves

As a hydrogen storage material, zeolites have aroused the concern because of the richness of adjustable, the characteristics of the diversity of channels. Metal-phosphate molecular sieves as a kind of important inorganic porous materials have been widely used in its selective catalysis, adsorption, separation and so on because of its unique structure and surface of the skeleton. So far, hydrogen adsorption has not been studied systematically besides only limited works were researched. Metal-phosphate molecular sieves provide a potential condition for hydrogen storage due to its structure.Metal-phosphate molecular sieves were synthesized by hydrothermal synthesis method in this paper. Tetraethyl ammonium hydroxide, methylamine, morpholine was as a template for the synthesis of AlPO₄-5, AlPO₄-53, SAPO-34 molecular sieve, respectively. Synthesis conditions of these molecular sieves were studied and synthesized samples were characterized by XRD, SEM and FT-IR. The thermal stability of these molecular sieves AlPO₄-5, AlPO₄-53, SAPO-34, ZnPO₄-HEX and ZrPO₄-Py were studied by XRD and TG. And then their hydrogen storage properties were tested at dry ice and liquid nitrogen temperature. The main results are listed as follows:Firstly, the molecular sieves AlPO₄-5 with 12-ring windows were synthesized in the hydrothermal system with tetraethyl ammonium hydroxide as the template agent. The conditions in the synthesis of molecular sieves AlPO₄-5 were: Al₂O₃: P₂O₅: TEAOH: H₂O =1:1: 0.6:40 (mol ration), the crystallization temperature of 150℃, crystallization time of three days. The SEM of AlPO₄-5 is a stack of a mass of plates. The hydrogen storage capacity of sample activated 6 hours at 500℃is 0.5 wt.% and 1.0 wt.% at 1.7 MPa, 195 K and 77K, respectively. This molecular sieve has a stead plat of release hydrogen at 195K.The hydrogen storage capacity increase with a linear current with the pressure increase at 77K.Secondly, the molecular sieves AlPO₄-53 were synthesized in the hydrothermal system with methylamine as a template agent. The composition of reaction is Al₂O₃: P₂O₅: CH₃NH₂:H₂O =1:1:1.25: 40 (mol ration), the crystallization temperature of 180℃, crystallization time of 3 days. The SEM of AlPO₄-53 is a stack of a mass of plates. The hydrogen storage capacity of sample activated 6 hours at 550℃is 0.52 wt.% and 1.40 wt.% at 1.7 MPa, 195 K and 77K, respectively. This molecular sieve has a stead plat of release hydrogen at 195K.The hydrogen storage capacity increase with a slightly current with the pressure increase at 77K.Thirdly, the molecular sieves SAPO-34 with 8-ring windows and better relatively were synthesized in the hydrothermal system with morpholine as a template agent. The composition of reaction is Al₂O₃: P₂O₅:SiO₂:C₄H₉NO: H₂O = 1:1.06: 1.08: 2.1: 66 (mol ration), the crystallization temperature of 200℃Crystallization of 2 days. The SEM of SAPO-34 is a cube up to 25×25×25μm. The hydrogen storage capacity of sample activated 6 hours at 550℃is 0.54 wt.% and 1.42 wt.% at 1.7 MPa, 195 K and 77K, respectively. This molecular sieve has a stead plat of release hydrogen at 195K.The hydrogen storage capacity increase with a slightly current with the pressure increase at 77K.Fourthly, The hydrogen storage capacities of (NH4) ZnPO₄-HEX molecular sieves activated 6 hours at 250℃is 0.50 wt.% and 0.68 wt.% at 1.7MPa, 195K and 77K , respectively. This molecular sieve has a stead plat of release hydrogen at 195K.The hydrogen storage capacity increase with a linear current with the pressure increase at 77K.Finally, The hydrogen storage capacities of ZrPO₄-py molecular sieves activated 6 hours at 450℃is 0.54 wt.% and 0.72 wt.% at 1.7MPa, 195K and 77 K. This molecular sieve has a stead plat of release hydrogen at 195K.The hydrogen storage capacity increase with a linear current with the pressure increase at 77K.