Kinetic investigation of solar chemical looping reforming of methane over Ni–CeO₂ at low temperature

Abstract

Leveraging solar thermal energy to drive the chemical looping reforming of methane (CLRM) is a promising method of efficiently and selectively reforming methane to produce syngas using renewable energy. In...

Enhanced syngas selectivity and carbon utilization during chemical looping reforming of methane via a non-steady redox cycling strategy

“…CLRM reactions were conducted in a horizontal packed-bed tube reactor system modified from prior work. 10,30 1.0 grams of 5 wt% Ni promoted CeO 2− δ (Ni-CeO 2− δ ) with a particle diameter range of 500 ≤ D p < 1400 μm were added to a 4 mm inner diameter alumina tube and held in position by alumina fiber. The Ni-CeO 2− δ synthesis process and material characterization under similar operating conditions are described in full in a previous publication.…”

“…(7) Neglect solid carbon formation. Each control volume is governed by the molar balance described in eqn (10). 31 The molar rate of change of each gaseous species (dn j /dt) is related to the molar ow rate entering and leaving each control volume (F j,in and F j,out , respectively) plus the molar rate of generation via chemical reactions (G j ).…”

“…22,23 Tradeoffs also exist with temperature; methane conversion generally increases while syngas selectivity decreases at higher operating temperatures. 10…”

“…9 CLR also exhibits robustness to catalyst poisoning and coke deposition because of adsorbate removal during oxidation. 10,11 When driven by solar process heat, CLR results in an energy upgraded syngas product serving as a solar energy storage solution. 12 Compared to solar thermochemical processes that directly split H 2 O and CO 2 , solardriven CLR can enable substantially higher solar-to-fuel conversion efficiencies (h s-f ) at lower, more manageable operating temperatures.…”

“…13 A recent on-sun demonstration of chemical looping reforming of methane (CLRM) reported record h s-f of up to 16% using CeO 2−d , 14 but for CLRM to be economically competitive with other reforming technologies h s-f must be further improved. Although there is extensive and ongoing materials development resulting in promising redox materials and surface enhancements to improve efficiency, 10,[15][16][17][18][19][20][21] it has also been shown for all nonstoichiometric materials that selectivity and conversion are signicantly impacted by the oxide nonstoichiometry (d, or oxygen deciency) during cycling. 11,15,[22][23][24] In general, it is understood that to enable high syngas selectivity and oxidant (CO 2 and/or H 2 O) conversion, the oxygen deciency should be high (i.e., d [ 0); yet, this comes at the expense of methane conversion which is most favorable at lower oxygen deciency.…”