The redox cycle of doped CaMnO3−δ has emerged
as an attractive way for cost-effective thermochemical energy storage
(TCES) at high temperatures in concentrating solar power. The role
of dopants is mainly to improve the thermal stability of CaMnO3−δ at high temperatures and the overall TCES
density of the material. Herein, Co-doped CaMnO3−δ (CaCo
x
Mn1–x
O3−δ, x = 0–0.5)
perovskites have been proposed as a promising candidate for TCES materials
for the first time. The phase compositions, redox capacities, TCES
densities, reaction rates, and redox chemistry of the samples have
been explored via experimental analysis and theoretical calculations.
The results demonstrate that CaCo0.05Mn0.95O3−δ showed an enhanced redox capacity (1000 °C
at pO2 = 10–5 bar) without
decomposition and provided the highest TCES density of ∼571
kJ kg–1 reported so far. The effective Co doping
tended to increase the valence states of B-site cations in perovskite
and facilitate the diffusion of the lattice oxygen atoms into the
surface-active oxygen sites. Furthermore, the high cooling rates deteriorated
the microstructure of CaCo0.05Mn0.95O3−δ particles and resulted in incomplete heat release, which is instructive
to the design and operation of the TCES systems.
The commonly used CuO/ZnO catalysts are prone to show unsatisfying performance at higher temperatures for hydrogen generation through methanol steam reforming (MSR) reaction, and thus catalyst modifications are required to enhance the performance of catalysts. In this study, CuO/ZnO was successfully loaded on a metal-organic framework material (Cu-BTC) by the impregnation method, with different masses of Cu-BTC. The catalyst ingredients and microstructure were characterized, and the catalytic performance at the temperature range from 200 to 340 °C was investigated in an MSR test system. The catalytic activity, anti-deactivation ability and stability performance of CuO/ZnO/Cu-BTCs were found to be much better than that of CuO/ZnO. The hydrogen concentration and hydrogen generation rate of CuO/ZnO/Cu-BTCs with 0.5 and 1 g Cu-BTC were increased by about 100% and 1 000%, respectively, comparing with the CuO/ZnO catalyst at 300 °C. Although superfluous Cu-BTC caused the evident reduction of catalytic activity at low temperatures, no obvious deactivation happened at higher temperatures. The deposition of CuO/ZnO on Cu-BTC has great potential to enhance the performance at higher temperatures for hydrogen generation through MSR reaction.
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