Browsing by Author "Lueking, Angela D."

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Observation and simulation of hydrogen storage via spillover
(2018-09-01)
Wang, Cheng-Yu
;
Chang, Cheng-Wei
;
Wu, Yi-Ju
;
Lueking, Angela D.
;
材料科學與工程學系
Hydrogen spillover refers to catalytic dissociation of hydrogen molecules followed by surface diffusion to the catalytic support. This mechanism has been proposed as a means to initiate hydrogen storage at ambient temperature. When catalytic dissociation of hydrogen is used to initiate room temperature hydrogen storage, this initiates weak chemisorption. High variations in experimental uptake, combined with theoretical calculations that are inconsistent with this mechanism, have made this concept controversial. Here, we review hydrogen uptake in porous carbon and metal-organic frameworks (MOFs), with emphasis on spectroscopic evidence of atomic hydrogen bound to the surface and resolution of discrepancies between experimental and theoretical studies. We conclude with a perspective of hydrogen spillover for future material design, hydrogen storage, and fundamental understanding of a process that is crucial for adsorption and catalysis.
Oxygen-selective adsorption in RPM3-Zn metal organic framework
(2017-06-29)
Wang, Cheng-Yu
;
Wang, Linxi
;
Belnick, Andrew
;
Wang, Hao
;
Li, Jing
Development of an oxygen selective adsorbent is anticipated to reduce the material and energy requirements for adsorptive separations of air by a factor of four, due to the relative concentrations of N-2 and O-2 in air, thereby decreasing the parasitic energy losses, carbon dioxide emissions, and cost of oxygen purification via pressure-swing adsorption. Here, we report that RPM3-Zn (a. k. a. Zn-2(bpdc)(2)(bpee); bpdc = 4,4'-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) is oxygen selective over nitrogen at temperatures from 77 K to 273 K, although the oxygen capacity of the sorbent decreased markedly at increasing temperatures. Due to an oxygen diffusivity that is similar to 1000-fold greater than nitrogen, the effective oxygen selectivity increases to near infinity at low temperature at equal contact times due to N2 mass transfer limitations for gate-opening. The kinetic limitation for N-2 to open the structure has a sharp temperature dependence, suggesting this effective kinetic selectivity may be "tuned in" for other flexible metalorganic- frameworks. Although the low temperature oxygen selectivity is not practical to displace cryogenic distillation, the results suggest a new mechanism for tailoring materials for kinetic selectivity, namely, capitalizing upon the delayed opening process for a particular gas relative to another. Published by Elsevier Ltd.