Preparation of SBA-15 supported Ru nanocatalysts by electrostatic adsorption-ultrasonic in situ reduction method and its catalytic performance for hydrogen storage of N-ethylcarbazole

N-ethylcarbazole (NEC) is an ideal liquid organic hydrogen storage carrier. The development of efficient hydrogen storage catalysts can promote the large-scale application of this process. In this paper, SBA-15 supported Ru nanocatalysts (Ru/S15-SU) were synthesized by strong electrostatic adsorption (SEA)-ultrasonic in situ reduction method (UR). Ru/S15-SU was characterized by N2 adsorption-desorption, TEM, H2 temperature program reduction, FT-IR, XRD, and XPS analysis measures. The results showed that ultrafine Ru NPs were evenly distributed on the surface of SBA-15, and ultrasonic in situ reduction not only reduced Ru3+ to Ru0, but also produced a coordination effect between Ru and O, enhancing the interaction between Ru NPs and the carrier. Ru/S15-SU exhibited excellent catalytic performance in the hydrogenation reaction of NEC, and the hydrogen storage efficiency reached 99.31% at 130°C and 6 MPa H2 pressure, which is superior to that of commercial 5wt%Ru/Al2O3. The excellent catalytic hydrogenation performance can be attributed to the selective anchoring of ruthenium ions on the surface of SBA-15 via electrostatic adsorption, preventing the aggregation of Ru NPs and enhancing the interaction between SBA-15 and Ru NPs by ultrasonic in situ reduction. Ru/S15-SU had a lower NEC hydrogenation apparent activated energy (Ea) of 68.45 kJ/mol than 5wt%Ru/Al2O3 catalyst. This method provides a new approach for the green preparation of nanocatalysts without using any chemical reducing agents.

A metal-organic framework with rich accessible nitrogen sites for rapid dye adsorption and highly efficient dehydrogenation of formic acid

MOFs with adequate free nitrogen sites have potential applications in dye adsorption and formic acid dehydrogenation. Here, we successfully synthesized a novel 3-D MOF 1 ([(CH₃)₂NH₂][Cd(L)DMA]·0.5DMA·1.5H₂O) with a special two-fold interpenetrating framework through a simple solvothermal reaction between CdCl₂·1.5H₂O and a nitrogen-rich triangular tricarboxylate-based linker (H₃L, 4,4',4''-s-triazine-2,4,6-tribenzoic acid). After removing the guest molecules of dimethylacetamide (DMA) and H₂O, including the coordinated DMA from 1 by vacuum activation at 423 K, a compound named 1' with a formula of [(CH₃)₂NH₂][Cd(L)] and a similar interpenetrating framework structure was obtained. In comparison with compound 1, the total void volume of 1' is nearly doubled, and thus may provide higher potential for the adsorption of other guest molecules. Notably, the pyridine N atoms located in the middle of the triangular tricarboxylate-based linker are not involved in the coordination with Cd²⁺, and are all uniformly dispersed throughout the whole framework of the 3-D MOFs. Due to its unique structural features, the 3-D MOF 1' could effectively adsorb the cationic dye MB⁺ for recycling purposes. The rapid adsorption rate (0.7 × 10^-2 g mg^-1 min^-1) and the relatively high capacity (900 mg g^-1) for MB⁺ demonstrate the potential of 1' in dye adsorption. In addition, 1' may also be used as an effective support to immobilize PdAu NPs via the double-solvent method. The resultant catalyst Pd0.8Au0.2/1' exhibits decent catalytic activity for the dehydrogenation of formic acid with a TOF value of 1854 h^-1 at 333 K. The existence of a large void volume and accessible pyridine N atoms provide a suitable environment for achieving a high dispersion of PdAu NPs, thereby leading to the formation of a catalytically active and stable supported noble-metal NP catalyst for H₂ generation from formic acid decomposition.

Experimental and Theoretical Studies of Ultrafine Pd-Based Biochar Catalyst for Dehydrogenation of Formic Acid and Application of In Situ Hydrogenation

In this work, a novel "foaming" strategy uses sodium bicarbonate (NaHCO₃) and ammonium oxalate ((NH₄)₂C₂O₄) as the foaming agent, turning biomass-derived carboxymethyl cellulose (CMC) into N-doped porous carbon. Highly active palladium nanoparticles (Pd NPs) immobilized on nitrogen-doped porous carbon (Pd@MC(2)-P) are produced through a phosphate-mediation approach. The phosphoric acid (H₃PO₄) becomes the key to the synthesis of highly dispersed ultrafine Pd NPs on active Pd-cluster-edge (the edge of the Pd-cluster-100 and Pd-cluster-111 surfaces). The Pd@MC(2)-P exhibits high activity for formic acid (FA) dehydrogenation with an initial TOF_g of 971 h^-1 at room temperature. The subsequent hydrogenation of phenol using FA as an in situ hydrogen source on Pd@MC(2)-P and the highly efficient hydrogenation of phenol to cyclohexanone reaches more than 90% selectivity and 80% conversion. Density functional theory (DFT) calculations reveal that the reduced H poisoning and more exposed (100) surface over Pd nanoparticles are the keys to the Pd nanoparticles' high activity.

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.

Bimetallic PdCo Nanoparticles Loaded in Amine Modified Polyacrylonitrile Hollow Spheres as Efficient Catalysts for Formic Acid Dehydrogenation

Polyacrylonitrile hollow nanospheres (HPAN), derived from the polymerization of acrylonitrile in the presence of polystyrene emulsion (as template), were modified by surface amination with ethylenediamine (EDA), and then used as support for loading Pd or PdCo nanoparticles (NPs). The resultant bimetallic catalyst (named PdCo0.2/EDA-HPAN) can efficiently catalyze the additive-free dehydrogenation of formic acid with very high activity, selectivity and recyclability, showing turnover frequencies (TOF) of 4990 h−1 at 333 K and 915 h−1 at 303 K, respectively. The abundant surface amino groups and cyano group as well as the hollow structure of the support offer a suitable environment for achieving high dispersion of the Pd-based NPs on the surface of EDA-HPAN, thus generating ultra-small bimetallic NPs (bellow 1.0 nm) with high stability. The addition of a small portion of Co may adjust the electronic state of Pd species to a certain extent, which can further improve their capability for the dehydrogenation of formic acid. In addition, the surface amino groups may also play an important role in synergistically activating formic acid to generate formate, thus leading to efficient conversion of formic acid to hydrogen at mild conditions.

Guanidinylated SBA-15/Fe3O4 mesoporous nanocomposite as an efficient catalyst for the synthesis of pyranopyrazole derivatives

In this study, a novel mesoporous nanocomposite was fabricated in several steps. In this regard, SBA-15 was prepared by the hydrothermal method, next it was magnetized by in-situ preparation of Fe3O4 MNPs. After that, the as-prepared SBA-15/Fe3O4 functionalized with 3-minopropyltriethoxysilane (APTES) via post-synthesis approach. Then, the guanidinylated SBA-15/Fe3O4 was obtained by nucleophilic addition of APTES@SBA-15/Fe3O4 to cyanimide. The prepared nanocomposite exhibited excellent catalytic activity in the synthesis of dihydropyrano[2,3-c]pyrazole derivatives which can be related to its physicochemical features such as strong basic sites (presented in guanidine group), Lewis acid site (presented in Fe3O4), high porous structure, and high surface area. The characterization of the prepared mesoporous nanocomposite was well accomplished by different techniques such as FT-IR, EDX, FESEM, TEM, VSM, TGA, XRD and BET. Furthermore, the magnetic catalyst was reused at least six consequent runs without considerable reduction in its catalytic activity.

Nanopore-Supported Metal Nanocatalysts for Efficient Hydrogen Generation from Liquid-Phase Chemical Hydrogen Storage Materials

Hydrogen has emerged as an environmentally attractive fuel and a promising energy carrier for future applications to meet the ever-increasing energy challenges. The safe and efficient storage and release of hydrogen remain a bottleneck for realizing the upcoming hydrogen economy. Hydrogen storage based on liquid-phase chemical hydrogen storage materials is one of the most promising hydrogen storage techniques, which offers considerable potential for large-scale practical applications for its excellent safety, great convenience, and high efficiency. Recently, nanopore-supported metal nanocatalysts have stood out remarkably in boosting the field of liquid-phase chemical hydrogen storage. Herein, the latest research progress in catalytic hydrogen production is summarized, from liquid-phase chemical hydrogen storage materials, such as formic acid, ammonia borane, hydrous hydrazine, and sodium borohydride, by using metal nanocatalysts confined within diverse nanoporous materials, such as metal-organic frameworks, porous carbons, zeolites, mesoporous silica, and porous organic polymers. The state-of-the-art synthetic strategies and advanced characterizations for these nanocatalysts, as well as their catalytic performances in hydrogen generation, are presented. The limitation of each hydrogen storage system and future challenges and opportunities on this subject are also discussed. References in related fields are provided, and more developments and applications to achieve hydrogen energy will be inspired.

Recent Advances in Noble Metal Catalysts for Hydrogen Production from Ammonia Borane

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.

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.

Efficient dehydrogenation of a formic acid-ammonium formate mixture over Au3Pd1 catalyst

A series of AuPd/C catalysts were prepared and tested for the first time for active and stable dehydrogenation of a formic acid-ammonium formate (FA-AF) mixture. The catalysts with different Au-to-Pd molar ratios were prepared using a facile simultaneous reduction method and characterized using transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that the catalytic activity and stability of the Au3Pd1/C catalyst was the best. The initial turnover frequency for the dehydrogenation of the FA-AF mixture over the Au3Pd1/C catalyst can reach 407.5 h-1 at 365 K. The reaction order with respect to FA and AF is 0.25 and 0.55, respectively. The apparent activation energy of dehydrogenation is 23.3 ± 1.3 kJ mol-1. The catalytic activity of the Au3Pd1/C catalyst remains ca. 88.0% after 4 runs, which is much better than the single Pd/C catalyst. The mechanism for the dehydrogenation is also discussed.

Palygorskite Supported AuPd Alloy Nanoparticles as Efficient Nano-Catalysts for the Reduction of Nitroarenes and Dyes at Room Temperature

In this work, AuPd alloy palygorskite based Pal-NH₂@AuPd nano-catalysts were prepared and used as catalysts for the reduction of nitroarenes and dyes at room temperature. The surface of palygorskite (Pal) was first modified with 3-aminpropyltriethoxysilane, and then covered with AuPd alloy nanoparticles through co-reduction of HAuCl₄ and K₂PdCl₄. The morphology and structures of the Pal-NH₂@AuPd nano-catalysts were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The as-synthesized Pal-NH₂@AuPd nano-catalysts displayed excellent catalytic performance in reducing 4-nitrophenol (4-NP) and various other nitroaromatic compounds. Moreover, the catalytic activities of the Pal-NH₂@AuPd nano-catalysts were adjustable via changing the atomic ratio of AuPd alloy nanoparticles, leading to the Pal-NH₂@Au₄₈Pd₅₂ component as having the best atomic ratio. The Pal-NH₂@Au₄₈Pd₅₂ continued to display good catalytic stability after being reused for several cycles and there were no obvious changes, either of the morphology or the particle size distribution of the nano-catalysts. Furthermore, these Pal-NH₂@Au₄₈Pd₅₂ nano-catalysts also provided a convenient and accessible way for the degradation of dyes in artificial industrial wastewater.

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.