Heterogeneous water phase catalysis as an environmental application: a review Kari Pirkanniemi a, * , Mika Sillanp€ a€ a b a Laboratory of Industrial Environmental Technology, Helsinki University of Technology, P.O. Box 6400, FIN-02015 Hut, Finland b Laboratory of Water Resources and Environmental Engineering, University of Oulu, P.O. Box 4300, FIN-90014, University of Oulu, Finland Received 29 August 2001; received in revised form 5 April 2002; accepted 5 April 2002 Abstract Catalytic water phase processes as an environmental application is a relatively novel subject with tremendous po- tential in the near future. This review of 120 references presents the wide scale of heterogeneous water phase appli- cations studied mainly within past five years. Both oxidation and hydrogenation processes are included as well as TiO 2 assisted photocatalysis. According to the references, heterogeneous catalysis is developing rapidly. New bimetallic catalysts and supports with higher surface area have improved catalytic efficiency in both oxidation and hydrogenation processes. It also seems that study on use of some waste materials such as red mud as catalyst is a very progressive field. On the whole, the chemical aspects are pretty well known, but the catalyst durability, and in many cases activity as well, has to be improved. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Environmental; Catalysis; AOP; Oxidation; Hydroprocessing; Wastewater 1. Introduction Scientific interest of catalytic water phase processes has awakened within past 10 years. For the time being catalytic water treatment processes are for very limited use only. However, ever tightening regulations in treat- ment of aqueous waste force to search novel methods in the near future. Many industrial waste streams are not suitable for biological processes due to their inherent toxicity, but their treatment by traditional non-catalytic chemical processes or by incineration may be too energy intensive. With adaptable catalyst, energy consumption of various well-known oxidation procedures e.g. super- critical water oxidation, wet peroxide oxidation, wet oxidation, and wet air oxidation of stable organics may be decreased (Luck, 1999; Larachi et al., 2001). Sup- posedly also novel procedures for degradation of stable compounds yet not efficiently degraded will arise. One interesting observation is advanced removal of nitrogen containing compounds in wet air oxidation when metal oxide catalyst is present (Deiber et al., 1997). Quality problems of groundwater and freshwater along with better understanding of importance of drink- ing water quality have already generated several studies dealing with heterogeneous catalytic raw water treat- ment processes including oxidation and hydrogenating processes. If catalyst in water phase process is dissolved a.k.a. homogeneous, separation processes possibly have to be adapted. In many cases, separation would be technically and/or economically unachievable. In addition, many active homogeneous catalysts, such as some metal salts are a potential environmental problem. Under these circumstances, there is a need for heterogeneous cata- lytic procedures where the catalyst is in different phase Chemosphere 48 (2002) 1047–1060 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +358-9-451-4213; fax: +358-9- 451-4213. E-mail address: kari.pirkanniemi@hut.fi (K. Pirkanniemi). 0045-6535/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(02)00168-6