Hydrogen Affinity of Silica-based Nanocomposite for High Temperature Hydrogen Separation Membranes
Authors: Ikuhara Yumi Hayami , Saito Tomohiro , Hataya Koji , Iwamoto Yuji , Takahashi Seiji 
Published: April 2011

Hydrogen Affinity of Silica-based Nanocomposite for High Temperature Hydrogen Separation Membranes Japan Fine Ceramics Center, 2-4-1, Mutsuno, Nagoya, 456-8587, Japan Yumi H. Ikuhara, Tomohiro Saito, Koji Hataya, Yuji Iwamoto and Seiji Takahashi Because of concerns about global warming, increasing attention is being directed to find an alternative to fossil hydrocarbon fuels and hydrogen is rapidly becoming one of the leading candidates. For hydrogen production, high temperature membrane reactor is applicable by simplify the process of producing hydrogen from natural gas and purifying it by combining these process into single step. Among the materials, ceramic membranes with molecular sieve-like properties have been expected for application in membrane reactors for conversion enhancement in dehydrogenation and methane reforming reactions. Amorphous silica (Si-O) membranes prepared by sol-gel method have been intensively studied as molecular sieve membranes for gas separation at high temperature. To enhance the hydrogen permselectivity, we have developed Ni nanoparticle-dispersed amorphous Si-O based composite membrane through the precursor solution method and achieved higher hydrogen permeance compared to helium and nitrogen at 573K to 773K. In order to understand the phenomenon of the high hydrogen permeance of the novel nanocomposite membrane, it is important to clarify the expected high temperature hydrogen affinity, i.e., hydrogen adsorption properties. Here, the relationship between microstructure and hydrogen affinity of the nanocomposite was intensively studied from the view point of concentration of Ni nanoparticle in the amorphous Si-O matrix and reversible hydrogen adsorption property. Ni nanoparticles with about 3 to 5 nm in size were homogeneously dispersed in the amorphous Si-O matrix, and the Ni nanoparticles reached to saturate in the Si-O matrix with Ni/(Si+Ni) ratio of 0.2. The reversibly adsorbed hydrogen was hardly detected on the amorphous Si-O and Ni at 573 K, while Ni nanoparticle-dispersed amorphous silica apparently exhibited reversible hydrogen adsorption property. There was appreciable pressure dependence of the reversible hydrogen adsorption on the composite. Further study of the relationship between the increase amount of the reversibly adsorbed hydrogen (Vr) and Ni content on the composite powders revealed that the Vr gradually increased with increasing the Ni content and the highest Vr was ascertained for the composite with the Ni/(Si+Ni) ratio of 0.2. Combining the results of the unique hydrogen permeance through the composite membrane and the hydrogen affinity in the composite powder, we conclude that the existence of reversibly adsorbed hydrogen due to the extensive dispersion of Ni nanoparticles in the Si-O-based membrane involve the enlargement of the number of solubility site for hydrogen, which resulted in the selective enhancement in the hydrogen permeance of the nanocomposite membrane. Contact persons: Y