Catalysis environmental applications

Adsorption, ion exchange, and catalysis share a great portion of environmental applications, as shown in the next section, and more extensively, in Chapter 2. Specifically, adsorption and catalysis are extensively used for the removal or destruction of air pollutants in gas streams as well as for purifying wastewaters or fresh water. Ion exchange has a special position among other techniques in the removal of heavy metals from wastewater. 

In the area of environmental application of catalysis, the most important processes are... 

Catalytic agents Mainly metals and metal oxides are used as the catalytically active components that are dispersed onto the support. The transition group elements and subgroup I are used extensively in environmental applications. Ag, Cu, Fe, Ni, their oxides, and precious metals like Pt, Pd, and Rh are a common choice in catalysis. 

Why adsorption, ion exchange and heterogeneous catalysis in one book The basic similarity between these phenomena is that they all are heterogeneous fluid-solid operations. Second, they are all driven by diffusion in the solid phase. Thus, mass transfer and solid-phase diffusion, rate-limiting steps, and other related phenomena are common. Third, the many aspects of the operations design of some reactors are essentially the same or at least similar, for example, the hydraulic analysis and scale-up. Furthermore, they all have important environmental applications, and more specifically they are all applied in gas and/or water treatment. 

An additional consideration in formulating redox reactions is the possibility of catalysis by substances that mediate the transfer of electrons between the bulk reductant (or oxidant) and the substrate being transformed. Such considerations arise frequently in many areas of chemistry, especially electrochemistry and biochemistry (e.g., 97). In environmental applications, the most common model for mediated electron transfer involves a rapid and reversible redox couple that shuttles electrons from a bulk electron donor to a contaminant that is transformed by reduction. 

A major aspect of research and development in industrial catalysis is the identification of catalytic materials and reaction conditions that lead to effective catalytic processes. The need for efficient approaches to facilitate the discovery of new solid catalysts is particularly timely in view of the growing need to expand the applications of catalytic technologies beyond the current chemical and petrochemical industries. For example, new catalysts are needed for environmental applications such as treatment of noxious emissions or for pollution prevention. Improved catalysts are needed for new fuel cell applications. The production of high-value specialty chemicals requires the development of new catalytic materials. Furthermore, new catalysts may be combined with biochemical processes for the production of chemicals from renewable resources. The catalysts required for these new applications may be different from those in current use in the chemical and petrochemical industries. 

Choi, H., E. Stathatos and D.D. Dionysiou (2006). Sol-gel preparation of mesoporous photocatalytic Ti02 films and Ti02/Al203 composite membranes for environmental applications. Applied Catalysis B-Environmental, 63(1-2), 60-67. 

Tronconi, E. Groppi, G. Structured Catalysts in environmental applications, 6th Topsoe Catalysis Forum 2009. Munkerupgaard Denmark, 2009 www.topsoe.com/sitecore/shell/ Applications/ /media/PDF%20files/Topsoe Catalysis Forum/2009/Tronconi.ashx. 

Hence, (photo)catalysis in environmental applications can be instrumental in promoting the quality of life and environment, in promoting a more efficient use of resources, and in promoting sustainable processes and products. 

It is an understatement to say that adsorption is a diverse field. It impacts separation processes, materials science, catalysis, soil science, pharmaceutical products, environmental applications, and other widely different fields. A brief overview of those subjects, mainly oriented toward applications, is presented here. 

The main drawback of kinetic models, based only on steady-state data, is associated with the fact, that start-up and transient regimes cannot be reliably modeled. Kinetic models for nonstationary conditions should be applied also for the processes in fluidized beds, reactions in riser (reactor) - regenerator units with catalyst circulation, as well as for various environmental applications of heterogeneous catalysis, when the composition of the treated gas changes continuously. 

K. Pirkanniemi, M. Sillanpaa, Heterogeneous water phase catalysis as an environmental application a review , Chemosphere, 48, 1047-1060, (2002). 

Ince NH, TezcanU G, Belen RK, Apikyan IG. (2001). Ultrasound as a catalyzer of aqueous reaction systems-the state of the art and environmental applications. Applied Catalysis B Environmental 29 167—176. 

Although there is little evidence for auto-catalysis in dechlorination by Fe , it is still possible that localized corrosion contributes to the remediation of contaminants in environmental applications. Various investigators have postulated that localized corrosion contributes through increased surface area (44) and creation of corrosion cell domains (49-51). The corrosion cell model works on the same principle as the electrochemical model described above (Figure 3), but invokes additional effects such as the reduction of protons as the major cathodic reaction, and the creation of an electrical double layer between the anode and cathode that permits transport due to electrical migration as well as diffusion. Although many aspects of these models are plausible, there are not yet any data that specifically support them, and a study that systematically addresses the role of localized corrosion in remediation applications of Fe remains to be done. 

Krzysztof Matyjaszewski received his PhD degree in 1976 from the Polish Academy of Sciences under Prof S. Penczek. Since 1985 he has been at Carnegie Mellon University where he is currently ). C. Warner University Professor of Natural Sciences and director of Center for Maaomolecular Engineering. He is also Adjunct Professor at the University of Pittsburgh and at the Polish Academy of Sciences. He is the editor of Progress in Polymer Science and Central European Journal of Chemistry. He has coedited 14 books and coauthored more than 70 book chapters and 700 peer-reviewed publications he holds 41 US and more than 120 international patents. His papers have been cited more than 50000 times. His research interests include controlled/living radical polymerization, catalysis, environmental chemistry, and advanced materials for optoelectronic and biomedical applications. 

In this contribution, we discuss the technical aspects of APXPS and give examples of its application to heterogeneous catalysis, environmental science, and electrochemistry. 

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