Brønsted acid sites based on penta-coordinated aluminum species

• DOI: 10.1038/ncomms13820
• Publication Date: 2016-12-15T13:25:32Z
• Authors: Zichun Wang; Yijiao Jiang; Olivier Lafon; Julien Trébosc; Kyung Duk Kim; Catherine Stampfl; Alfons Baiker; Jean-Paul Amoureux; Jun Huang
• Keywords: [CHIM.MATE] Chemical Sciences/Material chemistry; Science; Q; [CHIM.MATE]Chemical Sciences/Material chemistry; 02 engineering and technology; 0210 nano-technology; 01 natural sciences; Article; 0104 chemical sciences

AbstractZeolites and amorphous silica-alumina (ASA), which both provide Brønsted acid sites (BASs), are the most extensively used solid acid catalysts in the chemical industry. It is widely believed that BASs consist only of tetra-coordinated aluminum sites (AlIV) with bridging OH groups in zeolites or nearby silanols on ASA surfaces. Here we report the direct observation in ASA of a new type of BAS based on penta-coordinated aluminum species (AlV) by 27Al-{1H} dipolar-mediated correlation two-dimensional NMR experiments at high magnetic field under magic-angle spinning. Both BAS-AlIV and -AlV show a similar acidity to protonate probe molecular ammonia. The quantitative evaluation of 1H and 27Al sites demonstrates that BAS-AlV co-exists with BAS-AlIV rather than replaces it, which opens new avenues for strongly enhancing the acidity of these popular solid acids.