MnOx-Promoted PdAg Alloy Nanoparticles for the Additive-Free Dehydrogenation of Formic Acid at Room Temperature

Deciphering Photoinduced Catalytic Reaction Mechanisms in Natural and Artificial Photosynthetic Systems on Multiple Temporal and Spatial Scales Using X-ray Probes

Utilization of renewable energies for catalytically generating value-added chemicals is highly desirable in this era of rising energy demands and climate change impacts. Artificial photosynthetic systems or photocatalysts utilize light to convert abundant CO2, H2O, and O2 to fuels, such as carbohydrates and hydrogen, thus converting light energy to storable chemical resources. The emergence of intense X-ray pulses from synchrotrons, ultrafast X-ray pulses from X-ray free electron lasers, and table-top laser-driven sources over the past decades opens new frontiers in deciphering photoinduced catalytic reaction mechanisms on the multiple temporal and spatial scales. Operando X-ray spectroscopic methods offer a new set of electronic transitions in probing the oxidation states, coordinating geometry, and spin states of the metal catalytic center and photosensitizers with unprecedented energy and time resolution. Operando X-ray scattering methods enable previously elusive reaction steps to be characterized on different length scales and time scales. The methodological progress and their application examples collected in this review will offer a glimpse into the accomplishments and current state in deciphering reaction mechanisms for both natural and synthetic systems. Looking forward, there are still many challenges and opportunities at the frontier of catalytic research that will require further advancement of the characterization techniques.

Heterogeneous Catalysis in Production and Utilization of Formic Acid for Renewable Energy

As the cleanest energy source, hydrogen has been followed with interest by researchers around the world. However, due to the internal low density of hydrogen, it cannot be stored and used efficiently which limits the hydrogen application on a huge scale. Chemical hydrogen storage is considered as a useful method for efficient handling and storage. Due to its excellent safety, formic acid stands out. It is worth noting that the matter and energy conversion is established based on formic acid, which is not referred to in the previous documentation. In this review, the latest development of research on heterogeneous catalysis via production and application of formic acid for energy application is reported. The matter and energy conversion based on formic acid are both discussed systematically. More importantly, with formic acid as the node, biomass energy shows potential to be in a dominant position in the energy conversion process. In addition, the catalytic mechanism is also mentioned. This review can provide the current state in this field and the new inspirations for developing superior catalytic systems.

Carbon-coated silica supported palladium for hydrogen production from formic acid - Exploring the influence of strong metal support interaction

Hydrogen energy is one of the most promising energy carriers to solve the increasingly severe energy crisis. Formic acid decomposition (FAD) solves the storage and transportation problems of hydrogen gas since hydrogen can be produced from aqueous formic acid under mild conditions. To efficiently convert formic acid to hydrogen gas, chemical and structural modification of Pd nanoparticles or supports have been carried out, especially introducing the strong metal support interaction (SMSI). Herein, we synthesized core-shell structured SiO2@SC compounds as the supports to introduce SMIS to Pd/PdO nanoparticles. The relationship between FAD activity and SMSI is investigated. The SMSI between Pd/PdO nanoparticles and SiO2/SC is adjusted by altering the thickness of the carbon layer. The X-ray photoelectron spectroscopy shows that owing to the strong electron-attracting ability SiO2 core contributes to leading the Pd0 active site in an electron-deficient state. The thickness of the carbon layer controls the ratio of Pd0/PdO, which enhances the anti-poisoning ability of the catalyst. Owing to the electron-deficient state of Pd0 and optimal ratio of Pd0/PdO, the hydrogen desorption rate of FAD on Pd is enhanced, and the turn over frequency of Pd/SiO2@SC-1:3 catalyst reaches 1138 h-1, which is ten times higher than that of the pristine Pd/SC catalyst. These results are believed to guide the design and development of highly active Pd-based catalysts for hydrogen generation via FAD.

Pronounced effect of yttrium oxide on the activity of Pd/rGO electrocatalyst for formic acid oxidation reaction

A highly efficient and stable electrocatalyst comprised of yttrium oxide (Y₂O₃) and palladium nanoparticles has been synthesized via a sodium borohydride reduction approach. The molar ratio of Pd and Y was varied to fabricate various electrocatalysts and the oxidation reaction of formic acid was checked. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) are used to characterize the synthesized catalysts. Among the synthesized catalysts (Pd_yY_x/rGO), the optimized catalyst i.e., Pd₆Y₄/rGO exhibits the highest current density (106 mA cm^-2) and lowest onset potential compared to Pd/rGO (28.1 mA cm^-2) and benchmark Pd/C (21.7 mA cm^-2). The addition of Y₂O₃ to the rGO surface results in electrochemically active sites due to the improved geometric structure and bifunctional components. The electrochemically active surface area 119.4 m² g^-1 is calculated for Pd₆Y₄/rGO, which is ∼1.108, ∼1.24, ∼1.47 and 1.55 times larger than Pd₄Y₆/rGO, Pd₂Y₈/rGO, Pd/C and Pd/rGO, respectively. The redesigned Pd structures on Y₂O₃-promoted rGO give exceptional stability and enhanced resistance to CO poisoning. The outstanding electrocatalytic performance of the Pd₆Y₄/rGO electrocatalyst is ascribed to uniform dispersion of small size palladium nanoparticles which is possibly due to the presence of yttrium oxide.

Superaerophobic Resin-Grafted rGO Aerogel with Boosted Product Removal Delivering High-Performance Hydrogen Release at Ultrahigh Storage Density

Liquid hydrogen carriers featuring high hydrogen content, safety, and hydrogen release on demand have motivated great endeavors for sustainable hydrogen supply. Nonetheless, direct hydrogen release is limited by the ultralow hydrogen evolution rate, while the conventional manner of extra additive and solvent addition for promoting rates greatly deteriorates its hydrogen storage density. Thus, it is still challenging to simultaneously satisfy high-performance hydrogen release and high storage density. Herein, an aerophobicity surface-based gas-liquid interface reaction strategy is proposed, which renders rapid product removal to promote dehydrogenation, fundamentally circumventing the employment of additives and solvents. Accordingly, a hierarchically porous resin-grafted reduced graphene oxide aerogel is designed. It imparts superaerophobic surface to facilitate product detachment from reactive sites, and the structure-oriented interface reaction design provides product diffusion channels and reduced diffusion resistance. As a result, the aerogel harvests a record hydrogen evolution rate (347 mmol g^-1  h^-1 ) in an ultrahigh-density formic acid of 19.8 g L^-1 , around two times the rate promotion and ten times the density improvement compared to the state-of-the-art materials and systems. The strategy presents an approach for the dehydrogenation of liquid hydrogen carriers, e.g., formic acid, formaldehyde, and hydrazine hydrate, concurrently ensuring high-performance hydrogen release and high hydrogen storage density.

Preparation Strategy Using Pre-Nucleation Coupled with In Situ Reduction for a High-Performance Catalyst towards Selective Hydrogen Production from Formic Acid

Formic acid decomposition (FAD) is one of the most promising routes for rapid hydrogen (H2) production. Extensive efforts have been taken to develop efficient catalysts, which calls for the simultaneous regulation of the electronic structure and particle size of the catalyst. The former factor determines the intrinsic performance, while the latter corresponds to the active site utilization. Here, an effective preparation strategy, pre-nucleation coupled with in situ reduction, is developed to realize and well-tune both surface electronic states and particle size of the pallidum (Pd) catalyst. Benefiting from the structural merits, the as-prepared catalyst exhibits high mass-specific activity of 8.94 molH2/(gPd·h) with few carbon monoxide (CO) molecules, and the activation energy could reach a value as small as 33.1 kJ/mol. The work not only affords a highly competitive FAD catalyst but also paves a new avenue to the synthesis of ultra-fine metal nanoparticles with tailorable electronic structures.

Improved hydrogen evolution performance by engineering bimetallic AuPd loaded on amino and nitrogen functionalized mesoporous hollow carbon spheres

A highly efficient heterogeneous catalyst was synthesized by delicate engineering of NH₂-functionalized and N-doped hollow mesoporous carbon spheres (NH₂–N-HMCS), which was used for supporting AuPd alloy nanoparticles with ultrafine size and good dispersion (denoted as AuPd/NH₂–N-HMCS). Without using any additives, the prepared AuPd/NH₂–N-HMCS catalytic formic acid dehydrogenation possesses superior catalytic activity with an initial turnover frequency value of 7747 mol H₂ per mol catalyst per h at 298 K. The excellent performance of AuPd/NH₂–N-HMCS derives from the unique hollow mesoporous structure, the small particle sizes and high dispersion of AuPd nanoparticles and the modified Pd electronic structure in the AuPd/NH₂–N-HMCS composite, as well as the synergistic effect of the modified support.

Anchoring ultrafine AuPd on NH₂-functionalized and N-doped hollow mesoporous carbon spheres for formic acid dehydrogenation.

Silver nanomaterials: synthesis and (electro/photo) catalytic applications

In view of their unique characteristics and properties, silver nanomaterials (Ag NMs) have been used not only in the field of nanomedicine but also for diverse advanced catalytic technologies. In this comprehensive review, light is shed on general synthetic approaches encompassing chemical reduction, sonochemical, microwave, and thermal treatment among the preparative methods for the syntheses of Ag-based NMs and their catalytic applications. Additionally, some of the latest innovative approaches such as continuous flow integrated with MW and other benign approaches have been emphasized that ultimately pave the way for sustainability. Moreover, the potential applications of emerging Ag NMs, including sub nanomaterials and single atoms, in the field of liquid-phase catalysis, photocatalysis, and electrocatalysis as well as a positive role of Ag NMs in catalytic reactions are meticulously summarized. The scientific interest in the synthesis and applications of Ag NMs lies in the integrated benefits of their catalytic activity, selectivity, stability, and recovery. Therefore, the rise and journey of Ag NM-based catalysts will inspire a new generation of chemists to tailor and design robust catalysts that can effectively tackle major environmental challenges and help to replace noble metals in advanced catalytic applications. This overview concludes by providing future perspectives on the research into Ag NMs in the arena of electrocatalysis and photocatalysis.

Enhancing the feasibility of Pd/C-catalyzed formic acid decomposition for hydrogen generation – catalyst pretreatment, deactivation, and regeneration

Formic acid decomposition (FAD) generates H₂ at low temperatures. CO poisoning inhibits FAD but is lifted under oxidative treatment.

Amino-functionalized graphene oxide-supported networked Pd-Ag nanowires as highly efficient catalyst for reducing Cr(VI) in industrial effluent by formic acid

Cr(VI) pollution in wastewater has increasingly become a global environmental problem owing to its acute toxicity. Herein, we present the one-pot procedure for preparing the amino-functionalized (-NH₂) graphene oxide (GO-) supported networked Pd-Ag nanowires by co-reduction growth in polyol solution, which show the highly efficient catalytic performance with the excellent cycling stability for the catalytic Cr(VI) reduction by formic acid as an in-situ source of hydrogen at room temperature. The electron transfer from Ag and amino to Pd increases the electron density of Pd, which enhances the catalytic formic acid decomposition and subsequent the catalytic Cr(VI) reduction. The catalytic reduction rate constant of Pd₃Ag₁/GO-NH₂ is determined to be 0.0768 min^-1, which is much superior to the monometallic Pd/GO-NH₂ and Pd₃Ag₁/GO. This study provides a novel strategy to develop catalysts for the catalytic reduction of Cr(VI) to Cr(III) in the industrial effluent using formic acid as an in-situ source of hydrogen.

Zeolite-Encaged Pd-Mn Nanocatalysts for CO2 Hydrogenation and Formic Acid Dehydrogenation

A CO₂ -mediated hydrogen storage energy cycle is a promising way to implement a hydrogen economy, but the exploration of efficient catalysts to achieve this process remains challenging. Herein, sub-nanometer Pd-Mn clusters were encaged within silicalite-1 (S-1) zeolites by a ligand-protected method under direct hydrothermal conditions. The obtained zeolite-encaged metallic nanocatalysts exhibited extraordinary catalytic activity and durability in both CO₂ hydrogenation into formate and formic acid (FA) dehydrogenation back to CO₂ and hydrogen. Thanks to the formation of ultrasmall metal clusters and the synergic effect of bimetallic components, the PdMn_0.6 @S-1 catalyst afforded a formate generation rate of 2151 mol_formate  mol_Pd ^-1  h^-1 at 353 K, and an initial turnover frequency of 6860 mol H 2  mol_Pd ^-1  h^-1 for CO-free FA decomposition at 333 K without any additive. Both values represent the top levels among state-of-the-art heterogeneous catalysts under similar conditions. This work demonstrates that zeolite-encaged metallic catalysts hold great promise to realize CO₂ -mediated hydrogen energy cycles in the future that feature fast charge and release kinetics.

Anchoring IrPdAu Nanoparticles on NH2-SBA-15 for Fast Hydrogen Production from Formic Acid at Room Temperature

Hydrogen (H₂), a regenerable and promising energy carrier, acts as an essential role in the construction of a sustainable energy system. Formic acid (HCOOH, FA), a natural biological metabolic products and also accessible through carbon dioxide (CO₂) reduction, has a great potential to serve as a prospective H₂ supplier for the fuel cell. Herein, ultrafine and electron-rich IrPdAu alloy nanoparticles with a size of 1.4 nm are highly dispersed on amine-modified mesoporous SiO₂ (NH₂-SBA-15) and used as a highly active and selective catalyst for fast H₂ production from FA. The as-synthesized IrPdAu/NH₂-SBA-15 possesses superior catalytic activity and 100% H₂ selectivity with initial turnover frequency values of 6316 h^-1 with the additive of sodium formate (SF) and 4737 h^-1 even without SF at 298 K, comparable to the most effective heterogeneous catalysts ever published. The excellent performance of IrPdAu/NH₂-SBA-15 was not only ascribed to the combination of the electronic synergistic effect of trimetallic alloys and the strong metal-support interaction effect but also attributed to the amine (-NH₂) alkaline groups grafted on SBA-15, which is beneficial to boost the split of the O-H bond of FA.

Flexible and Adaptable Fuel Cell Pack with High Energy Density Realized by a Bifunctional Catalyst

A proton exchange membrane fuel cell (PEMFC) system with a hydrogen generator could have higher energy density than flexible batteries and supercapacitors and is possible to meet the urgent demand of flexible electronics. However, a flexible PEMFC pack is still not available due to the absence of a flexible hydrogen generator. To solve this problem, we successfully invented a flexible and adaptable hydrogen generator, which was realized by a new bifunctional aerogel catalyst with the abilities of both storing and producing hydrogen. The flexible hydrogen generator can produce hydrogen at room temperature when the device is inverting, bending, and rotating. By combining this flexible hydrogen generator and the unique flexible PEMFC stack of our group, we originally made a highly flexible and adaptable fuel cell pack with a high theoretical energy density (up to 722 Wh·kg^-1) and current achieved energy density (135.9 Wh·kg^-1). Such a PEMFC pack is highly promising to meet the high demand of flexible electronics.

Reclamation of hexavalent chromium using catalytic activity of highly recyclable biogenic Pd(0) nanoparticles

Hexavalent chromium is extremely toxic and increasingly prevalent owing to industrialisation, thereby posing serious human health and environmental risks. Therefore, new approaches for detoxifying high concentrations of Cr (VI) using an ultralow amount of catalyst with high recyclability are increasingly being considered. The catalytic conversion of Cr (VI) into Cr (III) was previously reported; however, it required a large amount of catalyst to reduce a low concentration of Cr (VI); further, pH adjustment and catalyst separation had to be performed, causing issues with large-scale remediation. In this study, an unprecedented eco-friendly and cost-effective method was developed for the synthesis of Pd nanoparticles (PdNPs) with a significantly narrow size distribution of 3-25 nm. PdNPs demonstrated the presence of elemental Pd with the zero oxidation state when analysed by energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The PdNPs could detoxify a high concentration of Cr (VI), without the need to adjust the pH or purify the nanoparticles for reusability. The reusability of the PdNPs for the catalytic conversion of Cr (VI) into Cr (III) was >90% for subsequent cycles without the further addition of formic acid. Thus, the study provides new insights into the catalytic reclamation of Cr (VI) for industrial wastewater treatment.

An amine-functionalized mesoporous silica-supported PdIr catalyst: boosting room-temperature hydrogen generation from formic acid

PdIr/SBA-15-NH₂ nanocomposites were synthesized via a facile surface functionalization and co-reduction method and used as a superior catalyst for complete and fast dehydrogenation of formic acid at room temperature.

Dehydrogenation of formic acid over Pd/C catalysts: insight into the cold plasma treatment

Non-thermal plasma treatment has great potential to open a fast and green route for controllable synthesis of highly active supported metal catalysts.

Chromium based metal–organic framework MIL-101 decorated palladium nanoparticles for the methanolysis of ammonia-borane

Pd@MIL-101 synthesized by a novel and facile approach acts as a highly active nanocatalyst (TOF = 1080 min⁻¹) in the methanolysis of ammonia-borane (NH₃BH₃) under air at room temperature.

Ultrafine PdAu nanoparticles immobilized on amine functionalized carbon black toward fast dehydrogenation of formic acid at room temperature

Ultrafine and highly dispersed PdAu nanoparticles were immobilized on amine functionalized carbon black (VXC-72-NH₂) for dehydrogenation of formic acid (FA). The introduction of amines is of vital importance for the formation of ultrafine PdAu nanoparticles (∼1.5 nm). Moreover, the presence of the amino groups also increased the electron density of PdAu nanoparticles, and this effect facilitated the formation of metal-formate, which further enhanced the rate of the catalytic dehydrogenation of FA. The as-prepared Pd_0.6Au_0.4/VXC-72-NH₂ exhibited high catalytic activity and 100% H₂ selectivity for dehydrogenation of formic acid without any additive, with turnover frequency (TOF) values of 7385 h^-1 at 298 K and 17 724 h^-1 at 333 K, which are the highest TOF values ever reported among heterogeneous catalysts for FA dehydrogenation.

Hydrogen Production from Formic Acid Attained by Bimetallic Heterogeneous PdAg Catalytic Systems

The production of H2 from the so-called Liquid Organic Hydrogen Carriers (LOHC) has recently received great focus as an auspicious option to conventional hydrogen storage technologies. Among them, formic acid, the simplest carboxylic acid, has recently emerged as one of the most promising candidates. Catalysts based on Pd nanoparticles are the most fruitfully investigated, and, more specifically, excellent results have been achieved with bimetallic PdAg-based catalytic systems. The enhancement displayed by PdAg catalysts as compared to the monometallic counterpart is ascribed to several effects, such as the formation of electron-rich Pd species or the increased resistance against CO-poisoning. Aside from the features of the metal active phases, the properties of the selected support also play an important role in determining the final catalytic performance. Among them, the use of carbon materials has resulted in great interest by virtue of their outstanding properties and versatility. In the present review, some of the most representative investigations dealing with the design of high-performance PdAg bimetallic heterogeneous catalysts are summarised, paying attention to the impact of the features of the support in the final ability of the catalysts towards the production of H2 from formic acid.

Anchoring Pt Single Atoms on Te Nanowires for Plasmon-Enhanced Dehydrogenation of Formic Acid at Room Temperature

Formic acid (HCOOH), as a promising hydrogen carrier, is renewable, safe, and nontoxic. However, the catalytic dehydrogenation of HCOOH is typically conducted at elevated temperature. Here, HCOOH decomposition is successfully achieved for hydrogen production on the developed Pt single atoms modified Te nanowires with the Pt mass loading of 1.1% (1.1%Pt/Te) at room temperature via a plasmon-enhanced catalytic process. Impressively, 1.1%Pt/Te delivers 100% selectivity for hydrogen and the highest turnover frequency number of 3070 h-1 at 25 °C, which is significantly higher than that of Pt single atoms and Pt nanoclusters coloaded Te nanowires, Pt nanocrystals decorated Te nanowires, and commercial Pt/C. A plasmonic hot-electron driven mechanism rather than photothermal effect domains the enhancement of catalytic activity for 1.1%Pt/Te under light. The transformation of HCOO* to CO2 δ -* on Pt atoms is proved to be the rate-determining step by further mechanistic studies. 1.1%Pt/Te exhibits tremendous catalytic activity toward the decomposition of HCOOH owing to its plasmonic hot-electron driven mechanism, which efficiently stimulates the rate-determining step. In addition, hot electrons generated by the Te atoms nearby Pt single atoms are regarded to directly inject into the reactants adsorbed and activated on Pt single atoms.

Palladium nanoparticles decorated on amine functionalized graphene nanosheets as excellent nanocatalyst for the hydrogenation of nitrophenols to aminophenol counterparts

We reported the improved catalytic property of Pd (0) nanoparticles decorated on amine-functionalized graphene nanosheets (Pd/GNS-NH₂) for the hydrogenation of nitrophenol derivatives in the presence of NaBH₄ at moderate conditions. Pd/GNS-NH₂ nanocatalyst was synthesized by the deposition-reduction method. Sundry techniques such as ICP-OES, P-XRD, XPS, TEM, HR-TEM and EDX have been applied to explain the structure and morphology of the Pd/GNS-NH₂ nanocatalyst. The results show that the Pd (0) nanoparticles are perfectly dispersed on the surface of the GNS-NH₂ support material (d_mean = 1.38-2.63 nm). The catalytic activity of the Pd/GNS-NH₂ nanocatalyst was tested in the hydrogenation of nitrophenol derivatives in water in the presence of NaBH₄ as reductant and the excellent activity of nanocatalyst have been detected against 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol derivatives with 116.8, 65.9, 42.8 and 11.4 min^-1 initial TOF values, respectively. Another important point is that the nanocatalyst has very high reusability performance (at 5th reuse between 71.5 and 91.5%) for the hydrogenation of nitrophenols. Finally, catalytic studies have been carried out at various temperatures to calculate the E_a, ΔH^≠ and ΔS^≠.

An effective amino acid-assisted growth of ultrafine palladium nanocatalysts toward superior synergistic catalysis for hydrogen generation from formic acid

An amino acid-assisted approach is developed to immobilize ultrafine Pd NPs onto mesoporous carbon, which exhibits remarkable catalytic activity for hydrogen generation.

Enhanced catalytic activity over palladium supported on ZrO2@C with NaOH-assisted reduction for decomposition of formic acid

Pd/ZrO₂@C was prepared employing UiO-66-derived ZrO₂@C as the support and showed high catalytic activity for formic acid decomposition.

Conformational twisting of a formate-bridged diiridium complex enables catalytic formic acid dehydrogenation

We previously reported that iridium complex 1a enables the first homogeneous catalytic dehydrogenation of neat formic acid and enjoys unusual stability through millions of turnovers. Binuclear iridium hydride species 5a, which features a provocative C2-symmetric geometry, was isolated from the reaction as a catalyst resting state. By synthesizing and carefully examining the catalytic initiation of a series of analogues to 1a, we establish here a strong correlation between the formation of C2-twisted iridium dimers analogous to 5a and the reactivity of formic acid dehydrogenation: an efficient C2 twist appears unique to 1a and essential to catalytic reactivity.

Atomic Layer Deposition of Ruthenium Nanoparticles on Electrospun Carbon Nanofibers: A Highly Efficient Nanocatalyst for the Hydrolytic Dehydrogenation of Methylamine Borane

We report the fabrication of a novel and highly active nanocatalyst system comprising electrospun carbon nanofiber (CNF)-supported ruthenium nanoparticles (NPs) (Ru@CNF), which can reproducibly be prepared by the ozone-assisted atomic layer deposition (ALD) of Ru NPs on electrospun CNFs. Polyacrylonitrile (PAN) was electropsun into bead-free one-dimensional (1D) nanofibers by electrospinning. The electrospun PAN nanofibers were converted into well-defined 1D CNFs by a two-step carbonization process. We took advantage of an ozone-assisted ALD technique to uniformly decorate the CNF support by highly monodisperse Ru NPs of 3.4 ± 0.4 nm size. The Ru@CNF nanocatalyst system catalyzes the hydrolytic dehydrogenation of methylamine borane (CH₃NH₂BH₃), which has been considered as one of the attractive materials for the efficient chemical hydrogen storage, with a record turnover frequency of 563 mol H₂/mol Ru × min and an excellent conversion (>99%) under air at room temperature with the activation energy ( E_a) of 30.1 kJ/mol. Moreover, Ru@CNF demonstrated remarkable reusability performance and conserved 72% of its inherent catalytic activity even at the fifth recycle.

Amine-functionalized graphene nanosheet-supported PdAuNi alloy nanoparticles: efficient nanocatalyst for formic acid dehydrogenation

PdAuNi/f-GNS provides CO-free hydrogen generation from additive-free dehydrogenation of formic acid even at room temperature.

Investigation on the enhanced catalytic activity of a Ni-promoted Pd/C catalyst for formic acid dehydrogenation: effects of preparation methods and Ni/Pd ratios

In this present work, we studied the effects of preparation methods and Ni/Pd ratios on the catalytic activity of a Ni-promoted Pd/C catalyst for the formic acid dehydrogenation (FAD) reaction. Two catalysts prepared by co-impregnation and sequential impregnation methods showed completely different Pd states and catalytic activities. As the sequentially impregnated catalyst showed better activity than the co-impregnated catalyst, the sequentially impregnated catalyst was investigated further to optimize the ratio of Ni/Pd. The highest catalytic activity for the FAD reaction was obtained over the seq-impregnated catalyst having a 1 : 1.3 molar ratio of Pd : Ni. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that small particle size is one factor improving the catalytic activity, while those of X-ray photoelectron spectroscopy (XPS) and X-ray adsorption near edge structure (XANES) indicate that the electronic modification of Pd to a positively charged ion is another factor. Thus, it can be concluded that the enhanced catalytic activity of the Ni-promoted Pd/C catalyst is attributed to the role of pre-impregnated Ni in facilitating the activity of Pd by constraining the particle growth and withdrawing an electron from Pd.

In this present work, we studied the effects of preparation methods and Ni/Pd ratios on the catalytic activity of a Ni-promoted Pd/C catalyst for the formic acid dehydrogenation (FAD) reaction.

AuPd Bimetallic Nanocrystals Embedded in Magnetic Halloysite Nanotubes: Facile Synthesis and Catalytic Reduction of Nitroaromatic Compounds

In this research, a facile and effective approach was developed for the preparation of well-designed AuPd alloyed catalysts supported on magnetic halloysite nanotubes (HNTs@Fe₃O₄@AuPd). The microstructure and the magnetic properties of HNTs@Fe₃O₄@AuPd were confirmed by transmission electron microscopy (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and vibrating sample magnetometry (VSM) analyses. The catalysts, fabricated by a cheap, environmentally friendly, and simple surfactant-free formation process, exhibited high activities during the reduction of 4-nitrophenol and various other nitroaromatic compounds. Moreover, the catalytic activities of the HNTs@Fe₃O₄@AuPd nanocatalysts were tunable via adjusting the atomic ratio of AuPd during the synthesis. As compared with the monometallic nanocatalysts (HNTs@Fe₃O₄@Au and HNTs@Fe₃O₄@Pd), the bimetallic alloyed HNTs@Fe₃O₄@AuPd nanocatalysts exhibited excellent catalytic activities toward the reduction of 4-nitrophenol (4-NP) to 4-aminophenol. Furthermore, the as-obtained HNTs@Fe₃O₄@AuPd can be recycled several times, while retaining its functionality due to the stability and magnetic separation property.

Surfactant-Free Synthesis of Carbon-Supported Palladium Nanoparticles and Size-Dependent Hydrogen Production from Formic Acid-Formate Solution

Steerable hydrogen generation from the hydrogen storage chemical formic acid via heterogeneous catalysis has attracted considerable interest given the safety and efficiency concerns in handling H₂. Herein, a series of carbon-supported capping-agent-free Pd nanoparticles (NPs) with mean sizes tunable from 2.0 to 5.2 nm are developed due to the demand for more efficient dehydrogenation from a formic acid-formate solution of pH 3.5 at room temperature. The trick for the facile size-controlled synthesis of Pd/C catalysts is the selective addition of Na₂CO₃, NH₃·H₂O, or NaOH to a Pd(II) solution to attain initial pH values of 7-9.5. For comparison, cuboctahedron modeling and electrochemical CO_ads stripping methods are applied to evaluate active surface Pd sites for turnover frequency (TOF) calculation. Both mass activity and specific activity (TOF) of hydrogen production are not only time-dependent but also Pd-size-dependent. An initial H₂ production rate of 246 L·h^-1·g_Pd^-1 is achieved on 2.0 nm Pd/C at 303 K, together with a TOF of 1815 h^-1 on the basis of cuboctahedron modeling of surface-active Pd sites. The initial TOF exhibits a significant rise from 3.5 down to 2.8 nm and then levels off below 2.8 nm and even shows a maxima at ca. 2.2 nm using the electrochemical surface area for calculation. The volcano-shaped dependence of TOF on Pd NP size may be better attributed to the changing ratios of terrace sites to defect sites on Pd NPs.

AgPd–MnOx supported on carbon nanospheres: an efficient catalyst for dehydrogenation of formic acid

AgPd and MnO_x nanoparticles were immobilized on biomass-derived carbon nanospheres, which exhibited excellent activity for the dehydrogenation of formic acid.

Phenylamine-functionalized mesoporous silica supported PdAg nanoparticles: a dual heterogeneous catalyst for formic acid/CO2-mediated chemical hydrogen delivery/storage

PdAg nanoparticles supported on phenylamine-grafted mesoporous silica acted as a dual heterogeneous catalyst for the interconversion of H₂ and CO₂.

Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH

Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst.