Brar Aneelman, Wang Xinran S, Gillis Ciara N, Yang Jenny Y, Findlater Michael
Department of Chemistry and Biochemistry, University of California, Merced 95343, California, United States.
Department of Chemistry, University of California, Irvine 92697, California, United States.
ACS Omega. 2025 May 20;10(21):21980-21984. doi: 10.1021/acsomega.5c02049. eCollection 2025 Jun 3.
CO is a potential feedstock for carbon-based fuels or materials, but is only available in dilute streams. Integrated processes for CO capture and conversion directly valorize the CO captured by sorbent materials, skipping the energetically expensive sorbent regeneration step. Amines are the most heavily studied liquid-phase sorbent materials for CO capture from dilute streams. Amines react with CO in a 2:1 ratio to form the corresponding ammonium carbamate. Ammonium carbamate [NH]-[HNCO] was tested as the substrate using the highly selective and robust CO-to-formate reduction electrocatalyst [(POCOP)-Ir-(H)-(NCCH)], where (POCOP) is the tridentate pincer ligand 2,6-bis-(di-butyl-phosphonito). When ammonium carbamate was used as the substrate instead of CO, only hydrogen was produced. An equivalent electrolysis with ammonium hexafluorophosphate with CO also resulted in primarily hydrogen. Methyl carbamate and urea were also tested as substrates as proxies for carbamate that do not contain an equivalent of ammonium, and there was also negligible reduction to carbon-based products. These results indicate that the loss of selectivity observed for amine-captured CO, or ammonium carbamate, is likely due to the generation of the acidic ammonium equivalent as well as the greater challenge of reducing carbamate compared to CO. This study illustrates that catalysts with high selectivity for concentrated CO can favor hydrogen evolution and loss of carbon-based products when amine-captured CO is used instead.
一氧化碳是碳基燃料或材料的潜在原料，但仅存在于稀释物流中。一氧化碳捕获与转化的集成工艺可直接将吸附剂材料捕获的一氧化碳转化为有价值的产品，跳过了能耗高昂的吸附剂再生步骤。胺类是从稀释物流中捕获一氧化碳研究最多的液相吸附剂材料。胺类与一氧化碳以2:1的比例反应形成相应的氨基甲酸盐。使用高选择性且稳定的一氧化碳到甲酸盐还原电催化剂[(POCOP)-Ir-(H)-(NCCH)]，将氨基甲酸盐[NH]-[HNCO]作为底物进行测试，其中(POCOP)是三齿钳形配体2,6-双-(二丁基膦酸酯)。当使用氨基甲酸盐代替一氧化碳作为底物时，仅产生氢气。用六氟磷酸铵与一氧化碳进行等效电解也主要产生氢气。还测试了氨基甲酸甲酯和尿素作为不含铵等效物的氨基甲酸盐的替代底物，还原为碳基产物的量也可忽略不计。这些结果表明，观察到的胺捕获的一氧化碳或氨基甲酸盐选择性丧失，可能是由于酸性铵等效物的产生以及与一氧化碳相比，还原氨基甲酸盐面临更大挑战。这项研究表明，当使用胺捕获的一氧化碳时，对浓缩一氧化碳具有高选择性的催化剂可能有利于析氢和碳基产物的损失。
