Selective Photocatalytic Dehydrogenation of Formic Acid by an In Situ-Restructured Copper-Postmetalated Metal–Organic Framework under Visible Light

Abstract

Formic acid is considered as one of the most promising liquid organic hydrogen carriers. Its catalytic dehydrogenation process generally suffers from low activity, low reaction selectivity, low stability of the catalysts, and/or the use of noblemetal-based catalysts. Herein we report a highly selective, efficient, and noble-metal-free photocatalyst for the dehydrogenation of formic acid. This catalyst, UiO-66(COOH) 2 -Cu, is built by postmetalation of a carboxylic-functionalized Zr-MOF with copper. The visible-lightdriven photocatalytic dehydrogenation process through the release of hydrogen and carbon dioxide has been monitored in real-time via operando Fourier transform infrared spectroscopy, which revealed almost 100% selectivity with high stability (over 3 days) and a conversion yield exceeding 60% (around 5 mmol•g cat −1•h −1 ) under ambient conditions. These performance indicators make UiO-66(COOH) 2 -Cu among the top photocatalysts for formic acid dehydrogenation. Interestingly, the as-prepared UiO-66(COOH) 2 -Cu hetero-nanostructure was found to be moderately active under solar irradiation during an induction phase, whereupon it undergoes an in-situ restructuring process through intraframework cross-linking with the formation of the anhydride analogue structure UiO-66(COO) 2 -Cu and nanoclustering of highly active and stable copper sites, as evidenced by the operando studies coupled with steady-state isotopic transient kinetic experiments, transmission electron microscopy and X-ray photoelectron spectroscopy analyses, and Density Functional Theory calculations. Beyond revealing outstanding catalytic performance for UiO-66(COO) 2 -Cu, this work delivers an in-depth understanding of the photocatalytic reaction mechanism, which involves evolutive behavior of the postmetalated copper as well as the MOF framework over the reaction. These key findings pave the way toward the engineering of new and efficient catalysts for photocatalytic dehydrogenation of formic acid.

H2 production from formic acid over highly stable and efficient Cu-Fe-O spinel based photocatalysts under flow, visible-light and at room temperature conditions

“…5A). Interestingly, a fourfold enhanced photocatalytic activity with respect to Cu [20]. In this study, the formation of highly active Cu 2 O/Cu 0 species trapped in the UiO-66 cages has been evidenced using highresolution HAADF-STEM images and XPS.…”

“…The first cycle manifests an induction period before reaching a steady state after 1 h with similar profiles of FAc conversion and CO 2 /H 2 production. probable [20]. This induction period totally disappears in the 2 nd cycle and the FAc conversion spontaneously reaches the steady state after irradiation (see Inserts Fig.…”

“…Alternatively, we have investigated a metal organic framework (MOFs) based materials for photocatalytic dehydrogenation of FAc [20]. The post-metalation of the MOFs structure with Cu and the in-situ restructuring of this latter during the reaction accounted for its high activity and the high selectivity of the reaction.…”

Active site imprinting on Ti oxocluster metal–organic frameworks for photocatalytic hydrogen release from formic acid

“…As stated earlier, to our knowledge, there are no precedents in the literature on the use of bare MOFs as active photocatalysts for the photocatalytic FA decomposition, while a recent study from El-Roz et al showed high potential for the UiO-66(Zr)-(COOH) 2 -Cu, where Cu-anhydride complex is at the origin of the activity. 53 As summarized in Table 1, H 2 evolution was also observed for these MOFs with a final H 2 production at 2 h of 260 and 360 μmol g photocatalyst −1 for the bare MIL-125(Ti) and UiO-66(Zr), respectively. This represents one half or less of the photocatalytic activity of fresh MIP-177-LT and about seven times lower than that of the highest performing MIP-177-LT-AT.…”

Molecular docking with SARS-CoV-2 and potential drug property of a bioactive novel Zn(II) polymer: A combined experimental and theoretical study

“…Various aromatic polycarboxylic acids have been extensively used as multifunctional building blocks in designing novel polymeric structures [25] , [26] . Among them, the o -phthalic acid (H 2 Phth) is a well-known versatile ligand, which is capable of chelating as well as bridging metal ions, thereby leading to the formation of polynuclear and low-dimensional systems [27] , [28] .…”