Multinuclear Solid-State NMR Study of Allophane

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  • Hatakeyama Moriaki
    Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University
  • Hara Takayoshi
    Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University
  • Ichikuni Nobuyuki
    Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University
  • Shimazu Shogo
    Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University

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Abstract

The structure of allophane heat-treated at 623, 773, and 973 K was characterized by 27Al cross-polarization magic-angle-spinning (CP-MAS) and 27Al multiple-quantum magic-angle-spinning (MQMAS) NMR. From these spectra, the structural change of allophane was observed over 623 K, i.e., the formation of five-coordinated Al from the original six-coordinated Al in allophane was confirmed after heat treatment. We concluded that Al atoms in the five-coordinated species have been formed by the OH elimination from six-coordinated Al in allophane. In addition, aluminosilicate layer deformation also took place to form silica and alumina thin layers separately. The results of 31P MAS NMR studies indicate the Lewis acid sites rather than Brønsted acid sites increased with a rise in the treatment temperature.

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