318 Research Article Received: 1 July 2014 Revised: 30 September 2014 Accepted article published: 3 November 2014 Published online in Wiley Online Library: 21 November 2014 (wileyonlinelibrary.com) DOI 10.1002/jctb.4585 The effect of deactivation of H-zeolites on product selectivity in the oxidation of chlorinated VOCs (trichloroethylene) Asier Aranzabal, * Manuel Romero-Sáez, Unai Elizundia, Juan Ramón González-Velasco and José Antonio González-Marcos Abstract BACKGROUND: The literature on the activity of diverse catalytic formulations for the oxidation of chlorinated volatile organic compounds is very large. Catalyst stability or durability has been investigated to a lesser extent, and particularly the effect of deactivation on selectivity, although it is a key factor for commercial scale applicability. RESULTS: H-zeolites suffered from rapid deactivation to some lower residual activity in the oxidation of trichloroethylene (TCE). The catalyst deactivation led to a decrease of selectivity to HCl and CO 2 , but to an increased selectivity for tetrachloroethylene (PER) and CCl 4 . By co-feeding water vapour, deactivation was avoided and the selectivity to PER and CCl 4 dropped near to zero. CONCLUSIONS: These effects were due to the loss of hydroxyl groups, which were partially chlorinated while TCE was adsorbed and decomposed. The selectivity data of PER and CCl 4 with time on stream (TOS) did not allow the conclusion that the formation of PER and CCl 4 took place by chlorination of TCE through HCl(g) or Cl 2 (g), as was previously suggested by some authors in the literature. It was concluded that formation of PER and CCl 4 takes place through the chlorination of TCE by chlorine species previously adsorbed on the surface of the zeolite. © 2014 Society of Chemical Industry Keywords: catalytic oxidation; chlorinated VOC; selectivity; deactivation; H-zeolite INTRODUCTION When researching environmental catalysts, those designed to abate emissions of hazardous compounds, the exhaust gas com- position should be carefully analyzed in order to ensure that the catalysts form intermediates that subsequently give harmless final reaction products and thus prevent the formation of toxic by-products. A significant problem in the design and operation of environmental catalytic processes is catalyst deactivation, i.e. the catalyst gradually loses the ability to convert pollutants into harmless compounds. The loss of catalyst activity is frequently accompanied by loss of selectivity, leading to higher levels of undesired by-products. The three major modes of deactivation, namely coking, poisoning and sintering, can all change the cata- lyst selectivity. 1,2 Coking and poisoning can alter selectivity either by disabling active sites and/or obstructing pores of the catalyst. The former may reduce the intrinsic rate of formation of one or more products while the latter may decrease the effective diffu- sivity of one or more reactants and/or products. Sintering may lead to a decrease in the number of active sites or even change the relative distribution of active sites. 3 The effect of deactivation on selectivity has been well researched in fields related to cat- alytic hydro-processing, 4 but it has been scarcely explored in envi- ronmental catalysis; particularly, in the oxidation of chlorinated volatile organic compounds (Cl-VOC). The selectivity of different catalysts has already been reported in the literature. 5 In general terms supported noble metals (Pt, Pd) and transition metal oxides (Cr 2 O 3 , Mn 2 O 3 , Co 2 O 3 ) catalysts, which are good oxidizing catalysts, are more selective to most oxidized products, such as CO 2 and Cl 2 and highly chlorinated products, such as tetrachlorethylene (PER). Nevertheless, acidic character catalysts, such as zeolites, are more selective to CO and HCl. The combination of acidic and oxidizing characteristics resulted in metal-doped zeolites having an intermediate selectivity towards the products mentioned above. The hydroxyl groups of the zeolites have been identified as the active centers for the adsorption and subsequent oxidation of Cl-VOCs. 6 – 9 The chemisorbed oxygen attack on the adsorbed molecule led to the formation of partially and/or fully oxygenated (but still adsorbed) species. These oxygenated species, including carbonyl, carboxylate and carbonate, were found to contain fewer chlorine atoms than the original feed molecule, which means that chlorine abstraction is an early step, probably the first step, for Cl-VOCs chemisorption. The catalytic activity for the formation of ∗ Correspondence to: Asier Aranzabal, Group “Chemical Technologies for Envi- ronmental Sustainability”, Chemical Engineering Dept, Faculty of Sciences and Technology, Universidad del País Vasco/EHU; P.O. Box 644, E-48080 Bilbao, Spain. E-mail: asier.aranzabal@ehu.es Group “Chemical Technologies for Environmental Sustainability”, Chemical Engineering Dept, Faculty of Sciences and Technology, Universidad del País Vasco/EHU, P.O. Box 644, E-48080 Bilbao, Spain J Chem Technol Biotechnol 2016; 91: 318–326 www.soci.org © 2014 Society of Chemical Industry