In this study, two different nano-structured samples of the FeTi compound were prepared by mechanical alloying and mechanical grinding. For these samples, kinetics of the initial rate of hydrogen absorption, and the equilibrium hydrogen pressure as a function of hydrogen concentration were measured. Mechanical alloying of Fe and Ti atoms produced the FeTi compound powder samples with microstructures of a mixture of nano-structured FeTi grains and amorphous phases. This sample exhibited a high initial rate of hydrogen absorption even at 298 K, however, a strongly reduced hydrogen storage capacity. Mechanical grinding of the FeTi produced samples of particles with a particular microstructure: surface layers with a mixture of nano-structured FeTi grains and amorphous phases, and a single crystalline phase of FeTi below the surface layers for each particle. This sample exhibited a high initial rate of hydrogen absorption without a significant reduction of the hydrogen storage capacity compared with that of the standard FeTi sample. This mechanical grinding treatment was found to be an effective method of surface modification to improve the initial activation of the FeTi hydrogen storage alloy.
DFT-based ONIOM calculations were employed to investigate
the potential energy surfaces (PESs) for the conversion of methane
to ethylene by a ZSM-5 zeolite containing a single coinage metal atom
whose formal charge is +1 (M-ZSM-5). According to the ONIOM calculations,
two methanes are activated by M-ZSM-5 to form ethylene and H2 via ethane. The mechanisms consist of the following elementary steps:
activation of a C–H bond of two methanes by M-ZSM-5 to form
CH3–M–CH3, a C–C bond formation
in CH3–M–CH3 to form ethane and
M-ZSM-5, and sequential activation of two C–H ethane bonds
by the regenerated M-ZSM-5 to form ethylene. Depending on the metal
cations, various active sites appear, reflecting whether Brønsted
acid sites (BASs) are formed after the alkane C–H activation.
Three types of active sites are present in Cu- and Ag-ZSM-5: metal
cations, methyl-metal (M–CH3) species, and BASs.
In contrast, the active sites in Au-ZSM-5 consist of Au cations or
H–Au–alkyl species. Looking at their PESs, we found
two energy-demanding steps: the second methane activation to form
CH3–M–CH3 for all M-ZSM-5 and
the second C–H bond activation of ethane by BASs (M = Cu and
Ag). We compared their activation energies to find that Cu- and Au-ZSM-5
are catalysts that are more suitable for forming ethylene from methane
and ethane, respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.