Prof. Constantinos G. Vayenas
Laboratory of Chemical and Electrochemical Processes
Department of Chemical Engineering
University of Patras
• B.S. (Diploma), Chemical Engineering N.T.U. Athens, 1973.
• Ph.D. Chemical EngineeringUniversity of Rochester, 1977.
Current Focus of Research:
Heterogeneous Catalysis and the role of Promoters.
Most commercial catalysts consist of an active metal or metal oxide phase, a support and one or more promoters. The latter play an important role by affecting the properties of the support or, more frequently, of the active phase. We have found that solid electrolytes can be used as active catalyst supports to induce dramatic and reversible changes in the catalytic properties of metals and metal oxides. This is accomplished by applying small voltages (1-2 V) between the conductive active phase and a counter electrode also deposited on the solid electrolyte. In this way promoting ions (O2-, F-, Na+, H+) are supplied in situ and reversibly on the active catalyst surface. The induced increase in catalytic rate is up to 200 times larger than the regular, unpromoted, rate and up to 3×105 larger than the rate of promoting ion supply. This new phenomenon, known in the literature as Electrochemical Promotion, or In situ controlled Promotion, or NEMCA (Non-Faradaic Electrochemical Modification of Catalytic Activity) permits a systematic and fundamental study of the role of promoters in Heterogeneous Catalysis. In addition to basic studies, we are currently exploring potential practical applications of the NEMCA effect in automotive catalysis (NOx reduction, CO and light hydrocarbon oxidation) and in industrial catalysis (selectivity enhancement in partial oxidation and hydrotreatment reactions).
A new type of gas recycle reactor-separator is being developed which allows for the partial oxidation of methane to ethylene or methanol/formaldehyde with very high yield. The recycled gas passes continuously through a molecular sieve trap in the recycle loop and the trapped valuable partial oxidation products are obtained by subsequent heating of the selective molecular sieve trap. In this way ethylene yield up to 85% has already been reached.
Electrocatalysis and Fuel Cells.
Fuel cells permit the direct conversion of a significant portion of the Gibbs free energy change of exothermic reactions into electricity rather than heat. We are currently investigating the development of new electrocatalytic anodes for the simultaneous production of valuable chemicals and electrical energy (chemical cogeneration). Parallel studies focus on the utilization of the NEMCA effect in aqueous electrochemistry.
Chemistry of concrete.
Concrete carbonation and chlorination are the main factors which limit the useful lifetime of reinforced concrete structures. The underlying physicochemical processes are studied and modelled in collaboration with Professor M. Fardis.