Synthesis, characterization, and catalytic activity of nitridated magnesium silicate catalysts
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Synthesis, characterization, and catalytic activity of nitridated magnesium silicate catalysts Katabathini Narasimharao • Mohamed Mokhtar Sulaiman N. Basahel • Shaeel A. Al-Thabaiti
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Received: 10 December 2012 / Accepted: 13 February 2013 / Published online: 22 February 2013 Ó Springer Science+Business Media New York 2013
Abstract Amorphous and crystalline magnesium silicates (MgSils) were prepared by sol–gel and templateassisted hydrothermal synthesis methods, respectively. The obtained materials were nitridated with NH3 at 300, 500, and 800 °C for 24 and 48 h generating nitridated MgSil catalysts. The catalysts were characterized by XRD, FTIR, TG–MS, N2-physisorption, Hammett indicators, and elemental analysis methods. MgSils nitridated at 300 °C were found to be more active for the Knoevenagel condensation reaction, compared to those nitradated at 500 or 800 °C. A larger amount of nitrogen was incorporated in the framework of amorphous MgSil compared to the crystalline MgSil. FTIR analysis indicated the presence of NHx species, which were known to form upon reaction between NH3 and M-OH groups. It was also found that the presence of Si–OH and Mg–OH groups along with the basic –NH2 functional groups is responsible for the enhanced catalytic activity of the low-temperature nitridated catalysts.
Introduction A considerable amount of research has been focused on new types of silicates with tunable properties due to their potential application in many areas including catalysis, gas adsorption, and separation [1]. Natural or synthetic aluminum and/or magnesium silicates belonging to the clay minerals group have industrial importance due to their
K. Narasimharao (&) M. Mokhtar S. N. Basahel S. A. Al-Thabaiti Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Kingdom of Saudi Arabia e-mail: [email protected]
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particular crystal structure, microfibrous morphology [2]. The magnesium ions in the crystal lattice of magnesium silicate clay-type materials are exchangeable with transition metal ions and the resultant materials are capable of adsorbing both acidic and basic ions [3]. These materials were tested as refining and purifying agents in the production of polyether polyols and found that they are excellent, deodorizing, potassium ion adsorbing agents [4]. Magnesium silicates, and its derivatives, were also used for advanced applications such as specific catalyst [5], fireretardant painting material [6], and a template for the synthesis of carbon nanofibers [7]. The structure of naturally occurring MgSil (Sepiolite) is derived from talc-like ribbons that expand with a width of three pyroxene chains. Each ribbon is connected to the next through an inverted Si–O–Si bond, resulting in a staggered talc layer with a continuous tetrahedral sheet and a discontinuous octahedral sheet. The discontinuous nature of the octahedral sheet allows for the formation of rectangular, tunnel-like micropores, which run parallel to the fiber axis and are filled completely
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