Surface acidity study of Mn+-montmorillonite clay catalysts by FT-IR spectroscopy: Correlation with esterification activity |
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| Affiliation: | 1. Department of Chemistry, Bangalore Institute of Technology, K.R. Road, V.V. Puram, Bangalore, Karnataka 560 004, India;2. Department of Chemistry, Bangalore University, Central College Campus, Bangalore, Karnataka 560 001, India;1. State Key Laboratory of High Performance Complex Manufacturing, College of Mechanical and Electrical Engineering, Central South University, Changsha, 410083, China;2. The Key Laboratory of Carcinogenesis and Cancer Invasion of the Chinese Ministry of Education, Cancer Research Institute and School of Basic Medical Sciences, Central South University, Changsha, 410013, China;3. Jiangxi University of Science and Technology, Nanchang, 330013, China;4. Shenzhen Institute of Information Technology, Shenzhen, 518172, China;1. School of Environmental Science and Engineering, Donghua University, shanghai 201620, China;2. School of Energy and Power Engineering, University of Shanghai for Science and Technology, shanghai 200093, China;1. Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100 Erzincan, Turkey;2. Vocational School of Health Services, Perfusion Techniques, Okan University, 34959 İstanbul, Turkey;3. Department of Chemistry, Faculty of Arts and Sciences, Recep Tayyip Erdoğan University, 53100 Rize, Turkey;1. State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China;2. Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, Jiangsu 210008, PR China;1. Department of Chemistry, University of Delhi, Delhi 110007, India;2. Department of Chemistry, University of Lucknow, Lucknow 226007, India;3. Department of Chemistry & Biochemistry and Centre for Nanoscience, University of Missouri-St. Louis, One University Boulevard, St. Louis, MO 63121-4499, USA |
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| Abstract: | A simple method for evaluating the surface acidity of different cation-exchanged montmorillonite (mont) clay catalysts, Mn+-mont (Mn+=Al3+, Fe3+, Cr3+, Zn2+, Ni2+, Cu2+, and H+), involving treatment with pyridine is described. After treating with pyridine, the samples were heated at 120 °C and the FT-IR spectra were directly recorded in the region 1650 and 1350 cm−1. The data obtained show the presence of both Lewis and Brønsted acid sites. The activities of the catalysts to bring about Brønsted acid catalysed esterification of succinic acid with iso-butanol to yield di-(iso-butyl) succinate have been studied. The Brønsted acidity data obtained for Mn+-mont correlated well with activity in the esterification reaction. The activities of the catalysts were found to decrease in the order of exchange ions Al3+ > Fe3+ > Cr3+ > Zn2+ > Ni2+ > Cu2+ > Na+-mont. They also correlated well with the charge to radius ratio of the cations. The catalysts exchanged with trivalent cations showed stronger absorption bands attributed to Brønsted acidity (1540 cm−1) whereas those exchanged with divalent cations showed an increased Lewis acidity (1450 cm−1) and reduced Brønsted acidity along with charge to radius ratio. Zn2+-, Cu2+- and Ni2+-exchanged clays showed an additional peak around 1605 cm−1 which is attributed to the pyridine adsorption on surface sites through its π electrons. The method suggested here to evaluate the acidity is suitable for active sites which are thermally unstable such as water molecules in the hydration shell of a cation in exchanged clay. |
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