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Abstract: The present experimental work deals with methane short contact time (SCT) CPO in a fixed bed reactor considering CH4 conversion and H2 and CO selectivity in a wide range of weight hourly space velocity (WHSV). Two different Rh/Al2O3-based catalysts both loaded with 0.5% by weight of Rh were developed: one catalyst carrying Rh on the external support surface (Egg-Shell configuration), and the other one with Rh embedded into the porous support (Egg-Yolk configuration). The goal was the design of the optimal fixed bed structure (not only considering beds made of egg-shell or egg-yolk catalysts alone, but also their various combinations), able to either attain the best performance or maintain a reaction temperature along the bed without excessive variations with WHSV. The highest CH4 conversion (>90%) and H2 selectivity (>98%), moreover stable despite the WHSV variation of about 3.6 times, and reactor working temperature with not too large variations (maximum of about 16%) by increasing WHSV were obtained with the fixed bed of Egg-Yolk catalyst alone. Instead, the fixed bed of Egg-Shell catalyst alone showed the worst performance: CH4 conversion and H2 selectivity were lower of about 15% and 10%, respectively, and decreasing with the increase of WHSV; on the contrary, the CO selectivity remained practically the same, only a slightly decrease being observed. Suitable combinations of the two catalysts in the fixed bed produced intermediate performance between those of the catalysts alone. The different performance of the two catalyst types was probably due to the different structure of the particles and to the Rh position on the carrier itself. Finally, thermal and performance durability tests up to 16 working hours showed that the Egg-Yolk catalyst employed alone in the fixed bed was able to maintain the CH4 partial oxidation activity with practically disregardable decrease. [Copyright &y& Elsevier]

Abstract: Catalytic combustion of CH4 or other gaseous HCs in microscale channels is becoming the key technology for various portable power generation devices that could replace current batteries to meet the increasing demand for more efficient, longer lasting and more environmentally friendly energy-consuming utilizations. New type of catalysts for the CH4/H2/air lean mixtures oxidation in drastic conditions were proposed and investigated; they were lined on SiC monoliths (dimensions 6mm×6mm×22mm) and tested into a lab-microreactor able to reach high power density (7.6MWth m−3). The catalysts were directly deposited on the monoliths via in situ solution combustion synthesis. The most interesting performance on the oxidation of CH4/H2/air lean mixtures was obtained with the monolith 2% Pt/(5% Al2O3), 2% Pd/(5% NiCrO4), followed by 2% Pd/(5% CeO2·ZrO2) and 2% Pd/(5% LaMnO3·ZrO2); the monolith 2% Pt/(5% Al2O3) behave better by burning CH4 or H2 alone. For the Pd-based catalysts, the addition of H2 to the reactive mixture led to an improvement of the CH4 combustion, whereas this did not happen for the Pt-based one. The addition of H2 to the gas mixture allowed to a decrease of the CH4-T50 and CH4-T100 compared to the combustion of CH4 alone, and the conversion curves slope becomes steeper: the higher the H2 concentration, the higher the mixture reactivity towards CH4 oxidation, probably due to the larger production of H2 reactive radicals (OHmple-para> [ABSTRACT FROM AUTHOR]

The combustion of CH(4)/H(2)/HC mixtures in a very small space represents an alternative, innovative way to produce thermal/electrical energy. Pd/NiCrO(4) catalysts are lined on SiC monoliths via in situ solution combustion synthesis (SCS), and the monoliths are then tested by feeding CH(4), H(2), and lean CH(4)/H(2) mixtures into a lab-scale test rig at an output thermal power of 7.6 MW(th) m(-3). In all cases, the combustion temperature shifts to values lower than those observed in non-catalytic combustion. When the power density is kept constant (by adding H(2) to the gas mixture), the value of CH(4)-T(50) (the half-conversion temperature of CH(4)) decreases relative to that of pure CH(4), and the slope of the conversion curve becomes steeper. The higher the H(2) concentration is, the higher the reactivity of the mixture towards CH(4) oxidation-probably due to a higher production of H(2) reactive radicals (OH).