Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-III-14MICRO-REACTORS FOR THE COMBUSTION OF METHANEA. Scarpa 1 , G. Landi 2 , R. Pirone 2 , G. Russo 11 Dipartimento di ingegneria chimica – Università Federico II di Napoli2 Istituto di Ricerche sulla Combustione – CNR – P.le Tecchio 80 – 80125 Naples (ITALY) –Fax: +39 0815936936 – e-mail: pirone@irc.cnr.itDespite the large use, the low energy density of conventional batteries is a limit in theminiaturization of the electronic devices induced by the advances in the fabrication techniquesin the area of MEMS [1]. Any fossil fuel shows an energy density at least 50 times higherthan a typical Li battery, so rendering the development of innovative processes of in-situelectricity generation via fuel combustion a very intriguing alternative for portableapplications, once an effective and relatively integrated efficient conversion system fromthermal to electrical power is applicable. Practical considerations related to fast and simplerecharge and low cost of liquid fuels render the required efficiency values not extremely high(i.e. 1-5%) to be successful. Thermoelectric (TE) or Thermo-photovoltaic (TPV) systems,based on the direct generation of electricity from fuel chemical potential rather thanthermodynamic cycles (and, consequently, moving parts) are showing very promising results[2]. Even if TE or TPV elements need high temperature to work efficiently, a high durabilityis exhibited by most common fabrication materials provided temperature does not exceed800 °C and even much lower in the case of thermoelectric conversion systems. Suchtemperatures are too low for a homogeneous combustion flame to be sustained, especiallyconsidering that the scales of interest in the field of the MEMS (1000-100 μm) approach thequenching distance for most possible fuels; so the application of a catalytic system appearsthe most attractive option. Actually, the use of a catalyst should guarantee a stable exercise ofthe process even in strongly diluted conditions, allowing a very uniform thermal profile too,with consequent improvements of conversion system efficiency.Micro-scale catalytic combustion has been receiving a lot of attention. In most cases,ceramic flat substrates supporting noble metals based catalysts have been investigated, mainlyin the combustion of hydrogen or very volatile liquid hydrocarbons, such as propane andbutane [3]. High volatility and low chemical and thermal stability does not render noble metalcatalysts very suitable for high temperature applications driving the research interests towardsless expensive transition metal mixed oxide based catalysts [4]. Despite its large diffusion,availability and consolidated distribution systems, few attentions have been devoted to thecombustion of methane, whose low reactivity requires higher temperatures for the completeconversion. Particular attention has been recently devoted to the study of the hydrogenmethanemixture providing high methane combustion rate, notwithstanding its relatively low117