Influence of Pd Precursor and Method of Preparation on Hydrodechlorination Activity of Alumina Supported Palladium Catal
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Influence of Pd Precursor and Method of Preparation on Hydrodechlorination Activity of Alumina Supported Palladium Catalysts Rajesh Gopinath Æ N. Seshu Babu Æ J. Vinod Kumar Æ N. Lingaiah Æ P. S. Sai Prasad
Received: 25 June 2007 / Accepted: 27 September 2007 / Published online: 16 October 2007 Springer Science+Business Media, LLC 2007
Abstract A series of alumina supported Pd catalysts were prepared by the novel deposition-precipitation method adopting the chloride precursor (DP-Cl) of Pd and varying the metal content from 0.25 to 1.0 wt%. The catalytic properties of prepared catalysts were studied by various characterization techniques such as N2 adsorption, CO chemisorption, TPR, XRD, XPS, and TEM techniques. The activity and stability of the catalysts were evaluated for the gas phase hydrodechlorination (HDC) of chlorobenzene operating at atmospheric pressure. At 1 wt% of Pd the catalyst showed higher chlorobenzene conversion with good stability when tested for a period of 25 h, whereas the other catalysts exhibited a loss in activity with time. In order to elucidate the exceptional activity and stability of this catalyst, a few more catalysts with 1 wt% Pd were prepared by impregnation technique and also using a nonchloride precursor, palladium nitrate. The 1 wt% DP-Cl catalyst again was found to be the best among the others. The activity and stability of the DP-Cl catalyst was also found to be superior to two low-dispersed catalysts, each with 10 wt% Pd, prepared by conventional impregnation method using the chloride and nitrate as the precursors. The characterization results reveal that the high activity and stability of the DP-Cl catalyst is related to the formation of electron deficient Pd species and its stabilization in the octahedral vacancies of alumina. Keywords Hydrodechlorination Chlorobenzene Pd/Al2O3 catalyst Deposition–precipitation
R. Gopinath N. Seshu Babu J. Vinod Kumar N. Lingaiah P. S. Sai Prasad (&) Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad, India e-mail: [email protected]
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1 Introduction Chlorinated hydrocarbons (CHCs), which possess unique physical and chemical properties, are extensively used commercially. However, when leaked into the atmosphere they form hazardous pollutants found largely in various waste organic liquids, emissions from a wide range of industrial processes and even in drinking water [1]. Among the various technologies proposed [2, 3] for treating these pollutants catalytic hydrodechlorination is adjudged as a simple, safe, effective methodology, which operates at low temperatures with limited toxic emissions. Among the noble metals, Pd is considered as the best catalyst for selective cleavage of the C–Cl bond [4, 5]. One of the main drawbacks of catalytic hydrodechlorination is the selective adsorption of HCl on the active sites causing deactivation of the catalyst [6]. Many researchers tried various ways to overcome the effect of HCl on the catalysts. A majority of publications suggest usage
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