Iridium Catalyst Immobilized on Crosslinked Polyethyleneimine for Continuous Hydrogen Production Using Formic Acid.

A series of spherical gold nanoparticles (AuNPs) stabilized by amphiphilic hyperbranched polymers, which have a hydrophilic hyperbranched polyethylenimine core and a hydrophobic shell formed by many long acidamide chains such as saturated palmitamide, octadecanamide, and unsaturated oleamide chains, were prepared by chemical reduction. The effect of the kinds and the ratio of the aliphatic chain in amphiphilic polymers, the amount of the amphiphilic polymers, and the storage time on their size, solubility, and stability in chloroform, toluene, petroleum ether, and n-butyl acetate was investigated by TEM, UV-vis. The results revealed that a high-concentration polymer with a double bond can greatly improve the organic solubility and stability of the AuNPs in the toluene, petroleum ether, and n-butyl acetate. All the AuNPs in different solvents could be used as highly efficient catalysts for the biphasic catalytic reduction of 4-nitrophenol. The effect of the concentration of AuNPs and the capping polymers, the volume of organic phase, and temperature on the turnover number (TON) values of AuNPs is also studied. Their TON values could be enhanced by the AuNPs capped with more polymers or selecting a good solvent. The maximum TON values of the AuNPs in different solvents are about 5040 which has never been reported in the heterogeneous catalytic reduction of 4-nitrophenol.

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.

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

The novel [Ru(Acriphos)(PPh3)(Cl)(PhCO2)] [1; Acriphos=4,5‐bis(diphenylphosphino)acridine] is an excellent precatalyst for the hydrogenation of CO2 to give formic acid in dimethyl sulfoxide (DMSO) and DMSO/H2O without the need for amine bases as co‐reagents. Turnover numbers (TONs) of up to 4200 and turnover frequencies (TOFs) of up to 260 h−1 were achieved, thus rendering 1 one of the most active catalysts for CO2 hydrogenations under additive‐free conditions reported to date. The thermodynamic stabilization of the reaction product by the reaction medium, through hydrogen bonds between formic acid and clusters of solvent or water, were rationalized by DFT calculations. The relatively low final concentration of formic acid obtained experimentally under catalytic conditions (0.33 mol L−1) was shown to be limited by product‐dependent catalyst inhibition rather than thermodynamic limits, and could be overcome by addition of small amounts of acetate buffer, thus leading to a maximum concentration of free formic acid of 1.27 mol L−1, which corresponds to optimized values of TON=16×103 and TOFavg≈103 h−1.

A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand tBu PNNOP (tBu PNNOP=2,6-(di-tert-butylphosphinito)(di-tert-butylphosphinamine)pyridine) (1) and the catalyst is readily prepared with MnBrCO5 to form [(tBu PNNOP)Mn(CO)2 ][Br] (2). Dehydrohalogenation of 2 generated the neutral five coordinate complex (tBu PNNOP)Mn(CO)2 (3). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h-1 , rivaling many noble metal systems. The parent chelate, tBu PONOP (tBu PONOP=2,6-bis(di-tert-butylphosphinito)pyridine) or tBu PNNNP (tBu PNNNP=2,6-bis (di-tert-butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [(tBu PONOP)Mn(CO)2 ][Br] (4) and [(tBu PNNNP)Mn(CO)2 ][Br] (5). FA dehydrogenation with the hybrid-ligand supported 2 exhibits superior catalysis to 4 and 5.

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.

The use of hybrids, developed by grafting homogeneous catalysts onto supporting materials, has already demonstrated significant potential in various catalytic processes. These systems combine the advantages of homogeneous catalysts, such as high activity and selectivity, with those of solid supports, including enhanced recyclability. Catalytic hydrogen (H2) production via dehydrogenation of C1 organic molecules targeting its use in fuel cells is a contemporary scientific issue directly connected with climate crisis. Here, Iminophospine hybrid [SiO2@benzNP] and its reduced analogue [SiO2@benzNHP] were synthesized, covalently grafted on colloidal SiO2, fully characterized (FT‐IR, RAMAN, TGA, ssNMR, BET), and used for in‐situ synthesis of [SiO2@benzNP‐FeII] and [SiO2@benzNHP‐FeII] catalytic complexes for H2 production from formic acid (HCOOH) and formaldehyde (HCHO), at 80 °C. In HCOOH, both heterogenized catalysts exhibit high selectivity, producing H2 and CO2 in a 1 : 1 ratio, without CO contamination, making them ideal for fuel cell applications. [SiO₂@benzNHP‐FeII] catalyst demonstrated superior performance in both substates. In HCOOH dehydrogenation, over 82,000 turnover number (TONs) were achieved and retained its efficiency for over five cycles, without any further metal addition. In HCHO dehydrogenation, it showed excellent efficiency as well, achieving 1.3 L of pure H2 with TONs exceeding 7,000, in 3 consecutive uses. Advanced spectroscopic analysis confirmed the stability and structural integrity of the catalysts, linking the Schiff base reduction and N−H groups to enhanced activity, durability and reusability. This study demonstrates the potential of hybrid materials with non‐noble metals for cost‐effective and sustainable H2 production, paving the way for scalable renewable energy solutions.

Water as a cocatalyst for photocatalytic H2 production 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.

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.

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).

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

A new class of bidentate phosphoramidite ligands, based on a spiroketal backbone, has been developed for the rhodium-catalyzed hydroformylation reactions. A range of short- and long-chain olefins, were found amenable to the protocol, affording high catalytic activity and excellent regioselectivity for the linear aldehydes. Under the optimized reaction conditions, a turnover number (TON) of up to 2.3×10(4) and linear to branched ratio (l/b) of up to 174.4 were obtained in the Rh(I)-catalyzed hydroformylation of terminal olefins. Remarkably, the catalysts were also found to be efficient in the isomerization-hydroformylation of some internal olefins, to regioselectively afford the linear aldehydes with TON values of up to 2.0×10(4) and l/b ratios in the range of 23.4-30.6. X-ray crystallographic analysis revealed the cis coordination of the ligand in the precatalyst [Rh(3d)(acac)], whereas NMR and IR studies on the catalytically active hydride complex [HRh(CO)(2)(3d)] suggested an eq-eq coordination of the ligand in the species.

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.

Ultrasmall PdAu alloy nanoparticles anchored on amine-functionalized hierarchically porous carbon as additive-free catalysts for highly efficient dehydrogenation of formic acid