Planejamento estatístico para avaliação da substituição parcial do Ni por Co e/ou Mn em catalisadores para reforma a seco do metano

Abstract

The dry reforming of methane - DRM is a promising technology, since it uses two of the greenhouse gases - GHG (CH4 and CO2) to obtain H2 or syngas (H2 + CO) which, besides being an interesting product from the industrial viewpoint, it can reduce GHG emissions to the environment. The use of nickelbased catalysts supported on non-reducible oxides such as alumina is very common in DRM. In general way, high conversion levels are reported for such catalysts, however, carbon offsets and nickel toxicity are still a problem. Active phases with more than one element have been investigated with the intention of potentiating the catalyst with the characteristics of its constituents, either to reduce cost, toxicity and coke, or to increase the conversion. In this context, statistical mixing planning is the best option to evaluate catalysts with active compound phase. In this work, it was used simplex-centroid statistical mixing planning with 50% restriction of the active phase composed of Ni and the other 50% of Ni, Co and Mn in different proportions following the experimental design adopted with the purpose of evaluating the synergistic and / or antagonistic effects on methane conversion, hydrogen yield, H2/CO molar ratio and cost of the active phase. The α-alumina, used as support, was obtained by microwave assisted self-combustion method and characterized by XRD, BET and SEM. The active phase was impregnated by wet way and the catalysts obtained were characterized by XRF, XRD (Before and after activation), TPR and SEM-EDS. The reducibility in H2 atmosphere and catalytic activity during the dry reforming reaction of the catalysts were investigated by in situ X-ray diffraction with monitoring of the exhaust gases. The catalytic tests were performed at 700 °C with a space velocity of 36 L.h -1 .g -1 and their data were used in the planning generating the mathematical models, which in turn, were used to model a catalyst named Cat mod. The main results show a good performance of Cat mod against the catalyst used as reference (Cat 1 -10% Ni) with cost reduction (- 35%) and toxicity, considering that there was a considerable reduction in the amount of Ni used . The Pareto diagram reports that any proportion of mixture between two of the studied elements results in an antagonistic effect, but when the three elements is combined, they have a synergistic effect. SEM and TGEGA characterized the catalysts after catalytic tests. The analyses after the catalytic tests show that Mn inhibits the formation of coke when used in amounts above 17 % (considering the composition of the active phase). Finally, a reaction mechanism was proposed that ideally illustrates the set of phenomena that compose the main reactions of the specific DRM for the catalysts studied in this work.