Enhanced Base‐Free Formic Acid Production from CO₂ on Pd/g‐C₃N₄ by Tuning of the Carrier Defects

Abstract

CO hydrogenation is attracting increasing attention as a sustainable route to produce formic acid, a commodity and potential energy vector. Here, bifunctional catalysts comprising metal nanoparticles deposited on bulk graphitic carbon nitride were assessed under base-free conditions, identifying supported Pd as the best performer. The catalyst productivity was enhanced by maximizing the edge-defects of the g-C N carrier, amino groups able to activate CO , and by generating welldispersed 5 nm Pd particles, required to split H . Bottom-up synthesis methods, that is, hard-templating and carbon enrichment upon polymerization, and top-down strategies, that is, thermal exfoliation of the as-prepared solid, were explored to boost the defects, the nature and density of which were evaluated by thermal and (in situ) spectroscopic techniques. After optimization of temperature, pressure, and reaction time, a 20 times higher turnover frequency compared with the best Pd/g-C N catalyst reported producing formic acid from CO without base was attained. This activity level was retained upon recycling with intermediate catalyst regeneration at mild temperature.

Zinc Oxide Morphology‐Dependent Pd/ZnO Catalysis in Base‐Free CO2 Hydrogenation into Formic Acid

“…However, the final product is formate instead of FA in the presence of base, which weakens the importance of this reaction. Currently, there are few reports of heterogeneous CO 2 hydrogenation into FA without the addition of base and the production rate of FA is also inferior [49–52] . Such as, Mondelli et al .…”

Efficient synthesis of highly dispersed ultrafine Pd nanoparticles on a porous organic polymer for hydrogenation of CO2 to formate

“…Heterogeneous catalysts, in spite of its merit in separation, have been scarcely reported on the formation of formic acid/ formate by hydrogenation of CO 2 due to poor catalytic performance. [26][27][28][29][30][31] Therefore, development of heterogeneous catalyst with well-dened properties is required in order to promote catalytic activity for the CO 2 hydrogenation and to enhance longterm stability performance. The metal-support interactions, between specic functional groups introduced into the support structures which enable tailoring the electronic and geometric properties, is promising design strategy for metal nanoparticles based catalysts.…”

Continuous Hydrogenation of Carbon Dioxide to Formic Acid and Methyl Formate by a Molecular Iridium Complex Stably Heterogenized on a Covalent Triazine Framework

“…[11b,c,16c,19] However, deconvolution of XPS spectra might add uncertainty to the data. [20] In order to unambiguously determine the molecular structure of the IrÀ CTF, extended Xray absorption fine structure (EXAFS) analysis of the Ir L 3 edge is performed in this study ( Figure 1). According to the Fourier transforms (FT) of k 2 -weighted EXAFS of the reference samples, IrCl 3 and Ir foil, the peaks at 1.90 and 2.55 Å can be assigned to IrÀ Cl and IrÀ Ir bonds, respectively.…”

“…Furthermore, in order to demonstrate continuous formic acid synthesis over the IrÀ CTF catalyst, water [20,24] or triethylamine [1] is co-fed into the reactor instead of methanol to create thermodynamically favorable environment for formic acid formation (Table 1). At 100°C, formic acid is selectively formed and its weight time yield (WTY) is much higher in triethylamine than in water, as expected from the stronger molecular interaction between the base and formic acid.…”

“…In literature, X-ray photoelectron spectroscopy (XPS) has been widely employed to study the chemical state of the metal center, carbon and/or nitrogen. [20] In order to unambiguously determine the molecular structure of the IrÀ CTF, extended Xray absorption fine structure (EXAFS) analysis of the Ir L 3 edge is performed in this study ( Figure 1). [20] In order to unambiguously determine the molecular structure of the IrÀ CTF, extended Xray absorption fine structure (EXAFS) analysis of the Ir L 3 edge is performed in this study ( Figure 1).…”