Manganese-Mediated Formic Acid Dehydrogenation.

Supported bimetallic catalysts have become an important class of catalysts in heterogeneous catalysis. Although well-defined bimetallic nanoparticles (BNPs) can be synthesized by seeded-growth in liquid phase, uniform deposition of these BNPs onto porous supports is very challenging. Here, we develop a universal nanoreactor strategy to directly fabricate the PdAu BNPs in the solid support of coral-like nitrogen-doped mesoporous polymer (NMP) with uniform dispersion in a large scale. This strategy is based on coordination chemistry to introduce the high-quality seeds of Pd nanoclusters and the Au ions into the NMP, and thus to be used as a nanoreactor for seeded growth of PdAu BNPs in solid state during thermal reduction. Many other supported Pd-based BNPs (diameters ranging from 2 to 3 nm) have also been successfully synthesized by adoption of this strategy, including PdRu, PdCo, PdNi, PdZn, PdAg and PdCu BNPs. As an example, the as-synthesized Pd1Au1/4 sample shows enhanced catalytic performance in formic acid (FA) dehydrogenation compared with the monometallic analogues, indicating the synergistic effect between Pd and Au. In addition, the Pd1Au1/4 product is molded into monolith without any binders due to its coral-like structure. The Pd1Au1/4 monolith shows considerable activity in FA dehydrogenation with a turnover frequency (TOF) value of 3684 h−1 at 333 K, which is recycled five times without changes in activity. We believe that the nanoreactor strategy provides an effective route to synthesize various supported bimetallic catalysts that have potential for applications in green and sustainable catalytic processes.

Water as a cocatalyst for photocatalytic H2 production from formic acid

Cold plasma for preparation of Pd/C catalysts toward formic acid dehydrogenation: Insight into plasma working gas

Spin-polarized density functional theory calculations have been performed to investigate formic acid dehydrogenation into carbon dioxide and hydrogen (HCO2H → CO2 + H2) on Ni(111). It is found that formic acid prefers the O (O═C) atop adsorption on nickel surface and the H (H–O) atom bridging two neighboring nickel atoms, and formate prefers the bidentate adsorption with O atop on nickel surface. The computed stretching frequencies for deuterated formic acid (DCO2H) and deuterated formate (DCO2) on Ni(111) agree well with the experimentally observed IR spectra. Formic acid dehydrogenation into surface formate and hydrogen atom (HCO2H → HCO2 + H) has barrier of 0.41 eV and is exothermic by 0.35 eV. Formate dehydrogenation into carbon dioxide and hydrogen atom (HCO2 → CO2 + H) has an effective barrier of about 1.0 eV and is the rate-determining step. Our computed adsorption configurations and energetic data for formic acid dehydrogenation on Ni(111) are very close to the reported results for Pt(111), but in sharp contrast to the previously reported results for Pd(111). Our recalculated adsorption configurations and energetic data for formic acid dehydrogenation on Pd(111) are similar to those on Ni(111) and Pt(111), demonstrating the high similarities of these metals. These computed data show that Pd-catalyzed formic acid dehydrogenation has the lowest effective barrier (0.76 eV), followed by Ni (1.03 eV) and Pt (1.56 eV).

Computational study on graphdiyne supported PdxCuy clusters as potential catalysts for formic acid dehydrogenation

The demand for harmless and efficient energy sources is remarkably expanding, particularly after the increased awareness of global warming, greenhouse gas emissions, immense fossil fuel consumption, and so forth. Formic acid is considered a potential candidate as an energy carrier for reversible hydrogen storage owing to its decomposition to hydrogen (H2) and carbon dioxide (CO2) in the presence of suitable catalysts. However, selective and efficient decomposition of formic acid using classical heterogeneous catalysis is still challenging because most heterogeneous catalysts which are known are ill defined. Herein, we report a promising heterogeneous approach toward formic acid dehydrogenation using a ruthenium PN3P pincer complex, [Ru–H(CO) (tBuPN3P)] (I), immobilized on a fibrous silica nanosphere, KCC-1, with a strong Lewis acid character [(≡Si–O–Si≡) (≡Si–O−)2Al–H]. The resulting heterogeneous catalyst, [Ru(H) (CO) (tBuPN3P)]@[(≡Si–O–Si≡) (≡Si–O−)2Al–H] (III), has been fully characterized by advanced solid-state characterization techniques. In this compound, Al is tetrahedrally coordinated. It is a single-site catalyst which exhibits good stability toward water, high pressures, and high temperatures as well as good activity in formic acid dehydrogenation. An excellent turnover number of 600,000 and a recyclability of up to 45 cycles are observed.

The storage and transportation of hydrogen gas, a non-polluting alternative to carbon-based fuels, have always been challenging due to its extreme flammability. In this regard, formic acid (FA) is a promising liquid organic hydrogen carrier (LOHC), and over the past decades, significant progress has been made in dehydrogenating FA through transition metal catalysis. In this review, our goal is to provide a detailed insight into the existing processes to expose various mechanistic challenges associated with FA dehydrogenation (FAD). Specifically, methodologies catalyzed by pincer-ligated metal complexes were chosen. Pincer ligands are preferred as they provide structural rigidity to the complexes, making the isolation and analysis of reaction intermediates less challenging and consequently providing a better mechanistic understanding. In this perspective, the catalytic activity of the reported pincer complexes in FAD was overviewed, and more importantly, the catalytic cycles were examined in detail. Further attention was given to the structural modifications, role of additives, reaction medium, and their crucial effects on the outcome.

Hydrogen is an alternative fuel that can play a critical role in achieving net zero emissions, leading to global environment sustainability. An iridium-immobilized catalyst based on polyethyleneimine (PEI) was synthesized and utilized for hydrogen production via formic acid dehydrogenation (FADH). Iridium complex is cross-linked with its ligand and PEI to form the immobilized catalyst, where the iridium content could be easily varied in the range of 1-10 %. The structure of the iridium-immobilized catalyst was confirmed using solid-state NMR, DNP NMR, and FTIR spectroscopies. The iridium-immobilized catalyst with PEI showed excellent catalytic activity for FADH, exhibiting the catalyst's highest turnover frequency (TOF) value of 73 200 h-1 and a large turnover number (TON) value of over 1 130 000. The catalyst could be used for continuous hydrogen production via FADH, exhibiting high durability for over 2 000 h with TON value of 332 889 without any degradation in catalytic activity. The obtained hydrogen gas was evaluated for power generation using a standard fuel cell, as well as achieved 5 h of stable power generation.

Formic acid is one of the most promising hydrogen carriers. Here, we report on a highly productive iridium-based catalyst for formic acid dehydrogenation, which is based on an underligated iridium(III) center containing a donor-flexible pyridylidene-amine ligand containing a chelating phenolate. This complex reaches temperature-dependent turnover frequencies from 2000 (40 °C) to 280000 h–1 (100 °C) and up to 3 million turnover numbers, thus outperforming state-of-the-art systems. The high efficiency together with the remarkably low cost and easy accessibility of the complex (<$100/g) are attractive features for industrial applications.

Synthesis of bimetallic 4-PySI-Pd@Cu(BDC) via open metal site Cu-MOF: Effect of metal and support of Pd@Cu-MOFs in H2 generation from formic acid

Development of hydrogen energy carriers is crucial for society. Reversible (de)hydrogenation using carbon-based materials, particularly formic acid (FA), has been widely studied. Typically produced under basic conditions through CO2 hydrogenation, formate salt is an energetically favorable form, but its dehydrogenation is challenging. This study found an equilibrium between formic acid dehydrogenation (FADH) and CO2 hydrogenation under high-pressure conditions, facilitated organic solvent suppression of dehydrogenation, and accelerated hydride formation on an Ir catalyst. These conditions allow for the direct production of FA from CO2 and H2 in nonbasic 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) using a pentamethylcyclopentadienyl iridium (Cp*Ir) catalyst featuring a 4,4′-diamino-2,2′-bipyridine ligand (4DABP). Under mild conditions (50 °C, 1 MPa; CO2:H2 ratio = 1:1), the catalyst achieved a turnover number (TON) of 2084 in 2 h. The use of supercritical CO2 further increased the TON to 6100, producing a 0.12 M FA solution after 96 h. This study presents a novel method for the direct production of formic acid from CO2 and H2, indicating new possibilities in the development of hydrogen energy carriers.

Catalytic degradation of halogenated contaminants by palladium (Pd) is a promising technology for environmental remediation. However, the low utilization of H by Pd catalyst and its easy poisoning prevent its applications. Here, low work function elements (B or Ag) were incorporated into Fe@C-supported Pd nanoparticles (NPs) to alter their crystalline structure and induce electronic effects, addressing these issues. The Pd mass-normalized dechlorination rates of trichloroethylene (TCE) by Fe@C-Pd-B and Fe@C-Pd-Ag were 51 and 59 times higher than that of unmodified Fe@C-Pd, respectively. The H utilization efficiency of Fe@C-Pd-B and Fe@C-Pd-Ag was 5.4 and 7.2 times higher than that of unmodified Fe@C-Pd, respectively. Various characterizations suggest that the B or Ag incorporation induced the charge redistribution and elevated the electron density of Pd atoms, resulting in the enhanced formic acid (FA) dehydrogenation and TCE dechlorination. Although the Ag incorporation presented a relatively higher H utilization due to the suppressed combination of H and accumulation of unsaturated hydrocarbons (i.e., C2H4), the Fe@C-Pd-Ag was easily deactivated. In contrast, the B incorporation enabled the Pd NPs with a good stability. These findings can guide the rational design of robust Pd-based catalysts for efficient and selective FA dehydrogenation and chlorinated contaminant degradation.

The [RuCl(dppe)2][OTf] (1) complex dehydrogenates formic acid under ambient conditions and results in the formation of trans-[Ru(η2-H2)Cl(dppe)2][OTf] (2) and trans-[Ru(η2-H2)H(dppe)2][OTf] (3) complexes. Addition of sodium formate to this reaction mixture increased the rate of formic acid dehydrogenation and complex 3 was obtained as the final product. Furthermore, complex 1 dehydrogenates formic acid catalytically in the presence of Hunig base. After several catalytic cycles, quantitative amounts of H2 and CO2 were produced at 298 K. The proposed formate bound intermediates cis-[2-Ru(HCO2)(dppe)2] were too unstable to be observable (or isolable), however, an analogous cis-[Ru(2-CF3CO2)(dppe)2][OTf] complex (6) was synthesized and characterized. This complex also dehydrogenates formic acid and led to the formation of complex 3. Based on NMR spectroscopic studies and other related chemical reactions, a plausible mechanism for formic acid dehydrogenation using complex 1 has been proposed. Moreover, 13C NMR spectral data on transfer hydrogenation of CO2 using complex 1 in presence of tert-butyl amine-borane (TBAB) as a secondary hydrogen source resulted in the amidation of CO2 to tert-butyl formamide.

Palladium-based catalysts are remarkable in endorsing hydrogen (H2) generation through formic acid (HCOOH, FA) dehydrogenation under near-ambient conditions. Hydrogen energy efficiency depends on high-performance catalyst design. In this study, Pd-Cu nanoalloy catalysts with mutable atomic ratios are successfully fabricated on TiO2 nanosheets (TiO2-NSs).The synergistic electronic interactions between Palladium (Pd) and copper (Cu) are revealed through a density of states (DOS) analysis of alloy supported over a mixed valence state of Ti linked to oxygen vacancies (Vo) in TiO2-NSs, Enhanced adsorption of target molecules reveals novel active sites for Formic acid dehydrogenation (FAD), with O─H bond cleavage via HCOO formate intermediate preceding C─H and C─O bond cleavage. Experimental and theoretical research demonstrates that the Pd-Cu/TiO2-NSs (3:7) catalyst d electron redistribution and d-band center shift lower the activation energy for O─H bond cleavage, exhibit superior H2 production than pure Pd and Cu, increasing Pd electron density due to synergistic effects from reactive crystal facets, defects, and strong metal support interactions (SMSI), lowering the activation energy for HCOOH dissociation step, generating carbon dioxide (CO2) and H2 with a unprecedented high turnover frequency (TOF) of 6268 molH2.h-1.molPd-1 at 303K with activation energy (Ea) of 15 KJ mol-1. This attempt models an efficient HCOOH-to-hydrogen catalyst.

Effect of the amine group content on catalytic activity and stability of mesoporous silica supported Pd catalysts for additive-free formic acid dehydrogenation at room temperature