The effects of H-2 concentration on the performance of a three-layer bed of Mo/HZSM-5 catalyst in nonoxidative methane dehydroaromatization at 1073 K and the distribution of coke formed along the bed were investigated systematically. Stepwise increasing the H-2 concentration up to 30% causes stepwise increases in C2H4 selectivity, while having little influence on benzene selectivity. Simultaneously, it also narrows the coke distribution by suppressing the formation of aromatic-type coke inside the zeolite channels and that of graphite-like C on the zeolite surface. The performance and coke distributions of one- and two-layer beds, together with the results obtained over the three-layer bed, showed that the cracking of C2H4 is more likely to dominate the coking process than the polycondensation of formed aromatics. Estimates of C2H4 approach to equilibrium for the reaction CH4 -> 1/2C(2)H(4) + H-2 confirmed that C2H4 always attains its equilibrium concentrations to ensure its availability for cracking. (C) 2015 Elsevier Inc. All rights reserved.