Hollow Mesoporous Organosilica Spheres Encapsulating PdAg Nanoparticles and Poly(Ethyleneimine) as Reusable Catalysts for CO2 Hydrogenation to Formate

Reaction and separation system for CO2 hydrogenation to formic acid catalyzed by iridium immobilized on solid phosphines under base-free condition

Hydrogenation of carbon dioxide (CO₂) to produce formic acid (HCOOH) in base-free condition can avoid waste producing and simplify product separation process. However, it remains a big challenge because of the unfavorable energy in both thermodynamics and dynamics. Herein, we report the selective and efficient hydrogenation of CO₂ to HCOOH under neutral conditions with imidazolium chloride ionic liquid as the solvent, catalyzed by a heterogeneous Ir/PPh₃ compound. The heterogeneous catalyst is more effective than the homogeneous one because it is inert in catalyzing the decomposition of product. A turnover number (TON) of 12700 can be achieved, and HCOOH with a purity of 99.5% can be isolated by distillation because of the non-volatility of the solvent. Both the catalyst and imidazolium chloride can be recycled at least 5 times with stable reactivity.

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

Hollow mesoporous nanoparticles with controllable size (less than 100 nm) are desired as drug-delivery carriers. Herein, we report the synthesis of monodispersed hollow mesoporous organosilica (HMOS) and hollow mesoporous silica (HMS) nanoparticles using soft and hard templating methods. HMOS shells, with 1,2-bis(triethoxysilyl)ethane (BTEE) as the precursor and hexadecyltrimethylammonium bromide and sodium dodecyl sulfate (SDS) as the soft templates, were formed on monodispersed silica nanoparticles (SNPs), which were used as the hard templates. HMOS and HMS nanoparticles were obtained by removing the SNPs after three rounds of ammonia dialysis. The hollow size of HMOS can be tuned by changing the size of the SNPs. By using SNPs with a size of 36.5 nm, hollow spaces of approximately 20 nm connected the surface through narrow pores (<5 nm). Mesopores of approximately 12 nm were formed by the surfactant micelles. Additionally, the interparticle space in HMOS and HMS was approximately 12 nm. The shell thicknesses of HMOS and HMS could be tuned in the range of 5-9 nm by changing the BTEE amount. Moreover, the amount of surfactant used varied the porous structure. The HMOS with a thickness of 5 nm exhibited a Brunauer-Emmett-Teller (BET) surface area of 268 m²/g and a total pore volume of 1.14 cm³/g. Meanwhile, HMS demonstrated a BET surface area of 553 m²/g and a total pore volume of 1.82 cm³/g while maintaining a hollow structure. HMOS displayed a high loading capacity for ibuprofen (3009 mg/g), and its drug release system showed a sustained-release property. Therefore, the HMOS preparation using hard and soft templates proposed herein can control the hollow size and shell thickness for drug-delivery applications.

Second Sphere Effects Promote Formic Acid Dehydrogenation by a Single-Atom Gold Catalyst Supported on Amino-Substituted Graphdiyne

Regulating the second sphere of homogeneous molecular catalysts is a common and effective method to boost their catalytic activities, while the second sphere effects have rarely been investigated for heterogeneous single-atom catalysts primarily due to the synthetic challenge for installing functional groups in their second spheres. Benefiting from the well-defined and readily tailorable structure of graphdiyne (GDY), an Au single-atom catalyst on amino-substituted GDY is constructed, where the amino group is located in the second sphere of the Au center. The Au atoms on amino-decorated GDY displayed superior activity for formic acid dehydrogenation compared with those on unfunctionalized GDY. The experimental studies, particularly the proton inventory studies, and theoretical calculations revealed that the amino groups adjacent to an Au atom could serve as proton relays and thus facilitate the protonation of an intermediate Au-H to generate H₂ . Our study paves the way to precisely constructing the functional second sphere on single-atom catalysts.

Ligand vacancy channels in pillared inorganic-organic hybrids for electrocatalytic organic oxidation with enzyme-like activities

Simultaneously achieving abundant and well-defined active sites with high selectivity has been one of the ultimate goals for heterogeneous catalysis. Herein, we construct a class of Ni hydroxychloride-based inorganic-organic hybrid electrocatalysts with the inorganic Ni hydroxychloride chains pillared by the bidentate N-N ligands. The precise evacuation of N-N ligands under ultrahigh-vacuum forms ligand vacancies while partially retaining some ligands as structural pillars. The high density of ligand vacancies forms the active vacancy channel with abundant and highly-accessible undercoordinated Ni sites, exhibiting 5-25 fold and 20-400 fold activity enhancement compared to the hybrid pre-catalyst and standard β-Ni(OH)₂ for the electrochemical oxidation of 25 different organic substrates, respectively. The tunable N-N ligand can also tailor the sizes of the vacancy channels to significantly impact the substrate configuration leading to unprecedented substrate-dependent reactivities on hydroxide/oxide catalysts. This approach bridges heterogenous and homogeneous catalysis for creating efficient and functional catalysis with enzyme-like properties.

Reaction-driven selective CO2 hydrogenation to formic acid on Pd(111)

Conversion of CO₂ to useful fuels and chemicals has gained great attention in the past decades; yet the challenge persists due to the inert nature of CO₂ and the wide range of products formed. Pd-based catalysts are extensively studied to facilitate CO₂ hydrogenation to methanol via a reverse water gas shift (rWGS) pathway or formate pathway where formic acid may serve as an intermediate species. Here, we report the selective production of formic acid on the stable Pd(111) surface phase under CO₂ hydrogenation conditions, which is fully covered by chemisorbed hydrogen, using combined Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC) simulations. The results show that with the full coverage of hydrogen, instead of producing methanol as reported for Pd(111), the CO₂ activation is highly selective to formic acid via a multi-step process involving the carboxyl intermediate. The high formic acid selectivity is associated with surface hydrogen species on Pd(111), which not only acts as a hydrogen reservoir to facilitate the hydrogenation steps, but also enables the formation of confined vacancy sites to facilitate the production and removal of formic acid. Our study highlights the importance of reactive environments, which can transform the surface structures and thus tune the activity/selectivity of catalysts.

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

Ordered periodic mesoporous organosilicas have been widely applied in adsorption/separation/sensor technologies and the fields of biomedicine/biotechnology as well as catalysis. Crucially, surface modification with functional groups and metal complexes or nanoparticle loading has ensured high efficacy and efficiency. This review will highlight the current state of design and catalytic application of transition metal-loaded mesoporous organosilica nanoreactors. It will outline prominent synthesis approaches for the grafting of metal complexes, metal salt adsorption and in situ preparation of metal nanoparticles, and summarize the catalytic performance of the resulting mesoporous organosilica hybrid materials. Finally, the potential prospects and challenges of metal-loaded mesoporous organosilica nanoreactors are addressed.

Porous PdAg alloy nanostructures with a concave surface for efficient electrocatalytic methanol oxidation

Tuning the composition and surface structure of the metal nanocrystals offered viable avenues for enhancing catalytic performances. Herein, we report a facile one-pot strategy for the formation of PdAg porous alloy nanostructures (PANs) with a concave surface. Due to their highly open nanostructures and tunable d-band center features, PdAg PANs exhibit superior electrocatalytic activity and long-term durability than Pd nanoparticles (NPs) and Pd/C for methanol oxidation reaction (MOR) in alkaline media. Our results provide a feasible and efficient approach for the controlled synthesis of high-performance Pd-based nanomaterials for alkaline MOR.

An air-stable, reusable Ni@Ni(OH)2 nanocatalyst for CO2/bicarbonate hydrogenation to formate

Production of formate via CO2/bicarbonate hydrogenation using cheap metal-based heterogeneous catalysts is attractive. Herein, we report the organometallic synthesis of a foam-like Ni@Ni(OH)2 composite nanomaterial which exhibited remarkable air stability and over 2 times higher catalytic activity than commercial RANEY® Ni catalyst in formate synthesis. Formate generation was achieved with an optimal rate of 6.0 mmol gcat-1 h-1 at 100 °C, a significantly lower operation temperature compared to the 200-260 °C reported in the literature. Deep characterization evidenced that this nanomaterial was made of an amorphous Ni(OH)2 phase covering metallic Ni sites; a core-shell structure which is crucial for the stability of the catalyst. The adsorption of bicarbonates onto the Ni@Ni(OH)2 catalyst was found to be a kinetically relevant step in the reaction, and the Ni-Ni(OH)2 interface was found to be beneficial for both CO2 and H2 activation thanks to a cooperative effect. Our findings emphasize the underestimated potential of Ni-based catalysts in CO2 hydrogenation to formate, indicating a viable strategy to develop stable, cheap metal catalysts for greener catalytic applications.

Surface functionalized highly porous date seed derived activated carbon and MoS2 nanocomposites for hydrogenation of CO2 into formic acid

In recent years, substantial progress has been made towards developing effective catalysts for the hydrogenation of CO₂ into fuels. However, the quest for a robust catalyst with high activity and stability still remains challenging. In this study, we present a cost-effective catalyst composed of MoS₂ nanosheets and functionalized porous date seed-derived activated carbon (f-DSAC) for hydrogenation of CO₂ into formic acid (FA). As-fabricated MoS₂/f-DSAC catalysts were characterized by FE-SEM, XRD, Raman, FT-IR, BET, and CO₂-TPD analyses. At first, bicarbonate (HCO₃^-) was successfully converted into FA with a high yield of 88% at 200 °C for 180 min under 10 bar H₂ atmosphere. A possible reaction pathway for the conversion of HCO₃^- into FA is postulated. The catalyst has demonstrated high activity and long-term stability over five consecutive cycles. Additionally, MoS₂/f-DSAC catalyst was effectively used for the conversion of gaseous CO₂ into FA at 200 °C under 20 bar (CO₂/H₂ = 1:1) over 15 h. The catalyst exhibited a remarkable TOF of 510 h^-1 with very low activation energy of 12 kJ mol^-1, thus enhancing the catalytic conversion rate of CO₂ into FA. Thus, this work demonstrates the MoS₂/f-DSAC nanohybrid system as an efficient non-noble catalyst for converting CO₂ into fuels.

Reverse water-gas shift reaction over Pt/MoOx/TiO2: reverse Mars–van Krevelen mechanism via redox of supported MoOx

Pt/MoO_x/TiO₂ shows excellent catalytic performance for the reverse water-gas shift reaction at 250 °C via reverse Mars–van Krevelen mechanism.