No abstract

The CO 2 desorption tests were conducted at 363-378 K for 5.0 mol/L blended monoethanolamine (MEA)-diethanolamine (DEA) solutions to develop the energy efficient solvents with high CO 2 production and low energy consumptions. These desorption tests were performed with a recirculation process for various preloaded, 5 mol/L (4.5 + 0.5 to 0.5 + 4.5) MEA-DEA solutions to find out the optimized solvents with minimum heat duty. Therefore, 1-4 mol/L and 0.5-0.45 mol/L MEA-DEA solvents have larger CO 2 production (nCO 2 ) and lower heat duties (H CO 2 ) than 5 mol/L DEA under similar operation conditions. They have lower heat duty (510 and 538 kJ/mol) than DEA (572 kJ/mol) due to increased CO 2 desorption rates, despite 10% higher heat input (Q Total ) than DEA. Moreover, the critical points were studied as research focus of amine regeneration curves, along with reaction energy calculation. Finally, secondary amines blending minor MEA (<20%) as promotor turned out to be an alternative approach of solvents improvement with low energy requirement.

Heat-duty reduction is the major challenge in CO 2 desorption and amine regeneration. The use of a combination of heterogeneous catalytic desorption with improved amine solvents is a novel approach to address this issue. We studied CO 2 -desorption tests of noncatalytic diethylamine (DEA) solvents as a benchmark and focused on five blended amines (DEA−monoethanolamine, MEA; 4.5:0.5 to 2.5:2.5 M) with three types of catalysts (γ-Al 2 O 3 , H-ZSM-5, and 2:1 blended γ-Al 2 O 3 −H-ZSM-5) to explore the synergy effects of DEA-based amine blends with solid catalysts. The heat duty and CO 2 production of each case scenario were tested for six sets of solutions with initial loading of 0.5 mol of CO 2 per mole of amine at 363−378 K and were compared with those of 5 M DEA solvents. The results showed that the three catalyst conditions (blended catalyst, H-ZSM-5, and γ-Al 2 O 3 ) followed different trends at rich and lean loadings. Finally, both 5 M DEA and 4.5:0.5 M DEA−MEA with blended catalysts exhibited very low heat duties of 151.2 and 168.0 kJ per mole of CO 2 at loadings of 0.50− 0.20 mol per mole of amine at 378 K among the six solutions. Both approaches proved to be the most-energy-efficient amine solutions whereas the blended amine with blended catalysts was the best strategy that was applicable in the CO 2 desorber.

in alkaline media) in the C2 pathway involved only 4 electrons. Apparently, a much higher energy efficiency could be obtained under the C1 pathway. Second, traditional Pt-based and Pdbased materials were long recognized as outstanding catalysts for EOR. [1b,3] Nevertheless, 4-electron process (namely C2 pathway) is still predominant so far. Their apparent C1-pathway faraday efficiency (FE) was rather low at room temperature (normally only ≈1-3%), [1a,3b,4] even if a ≈26% C1-pathway FE in alkaline media on Pd-Ni(OH) 2 /rGO was obtained. [5] Therefore, fabricating advanced electrocatalysts that efficiently break the CC bond and easily oxidize as-formed C1 intermediates into CO 2 is crucial and urgent, but irrelative research is far limited now. Fortunately, R. R. Adzic's group [6] first reported a milestone work of PtRhSnO 2 /C catalyst, and they indicated that Rh component could play a crucial role in breaking the CC bond of ethanol, which has also been discovered in organic synthesis by Dong et al. [7] From then on, some Rh-based EOR catalysts (using Rh as the main catalyst) such as Rh/C coated on Foam Ni, [8] Rh/CeO 2 , [9] cyclic penta-twinned Rh nanobranches, [10] Rh-Ni alloy, [11] and Rh-contained EOR catalysts like PtRhCu cubic nanoboxes [12] and octahedral PtNiRh nanoparticles [13] have been successively reported. However, their EOR activities are too low to meet the practical requirements of DEFCs. The main problem for Rh-based EOR catalysts could be the sluggish oxidation of as-generated C1 intermediates (CO ad and CH x species) on Rh surface, which has been proposed in our previous in situ surface-enhanced infrared absorption spectral (SEIRAS) investigation. [14] According to the proverbial Langmuir-Hinshelwood Mechanism, it may be solved by introducing some oxophile components around the Rh nanodomain. As far as we know, lead (Pb) is an oxophile metal, which may provide abundant oxygen-contained species (OH ad species) to oxidize the adsorbed C1 intermediates. Actually, previously reported platinum-lead oxide nanocomposites (Pt-PbO x) show much higher EOR activity than pristine Pt nanoparticles. [15] Furthermore, surface-adsorbed Pb was recognized as a promoter for breaking the ethanol CC bond. [16] Based on these considerations, it may be expected that a considerable EOR catalysis performance can be obtained Rhodium (Rh)-based catalysts may solve the long-standing inefficient oxidation of ethanol for direct ethanol fuel cells (DEFCs); however, the performance of ethanol oxidation reaction (EOR) on existing Rh-based catalysts are far limited. Herein, the Rh-Pb catalysts are synthesized by building Pb and Pb oxide around Rh nanodomain, which shows highly efficient splitting CC bond and facile further oxidation of as-generated C1 intermediates (CO ad and CH x fragments). It exhibits an ever-highest EOR peak mass activity of ≈2636 mA mg −1 Rh among Rh-based catalysts in alkaline media. Meanwhile, its anodic current remains ≈50% even after a 4 h durability test at 0.53 V versus RHE. As for the C1-pathwa...