Thin-sheet microfibrous-structured Pd-MgO-Al2O3/Al-fiber catalysts were developed for high-throughput catalytic methane combustion with 3-15 vol% water vapor in feed gas. The catalysts were obtained by hydrothermally growing Mg-Al mixed-oxide precursors (e.g., layered double hydroxides (LDHs) plus MgCO3) on Al-fiber surfaces followed by placing 0.5 wt% Pd on the as-obtained substrates by impregnation. Transformation of Pd/MgAl-LDH-MgCO3 mounted on the Al-fiber into Pd-MgO-Al2O3 via in situ reaction activation markedly enhances the catalyst basicity and electron density of metallic Pd, thus weakening support electrophilicity and stabilizing PdO against the formation of inactive Pd4+ species. This preferred catalyst with high intrinsic activity (turnover frequency 135 h(-1) at 290 degrees C and 3 vol% water vapor) achieves a very low Ea of only 57 kJ mol(-1), a third that (170 kJ mol(-1)) for the Pd/AlOOH/Al-fiber. This catalyst can stably run for feed gases of 1 vol% methane and 3-15 vol% water vapor in air. (C) 2020 Elsevier Inc. All rights reserved.