Highly dispersed PdAg nanoparticles supported on phenylamine-functionalized mesoporous carbon were synthesized and assessed as bifunctional heterogeneous catalysts for the interconversion of formic acid (FA) and CO2 in chemical hydrogen storage systems. A high turnover frequency (TOF) of 5638 h–1 for evolved H2 on the basis of the total amount of Pd in the sample was obtained during the dehydrogenation of FA, corresponding to a TOF value of 21686 h–1 on the basis of the quantity of surface Pd atoms. In addition, this material promoted the hydrogenation of CO2 to FA with a turnover number (TON) of 839 over 24 h for produced FA on the basis of the total amount of Pd, corresponding to a TON of 3227 on the basis of the quantity of surface Pd atoms. Both the synergistic alloying effect and the surface functionalization with weakly basic phenylamine molecules were vital aspects of these high catalytic activities. Experimental and theoretical studies revealed that the cooperative action of the phenylamine groups in the vicinity of active PdAg NPs significantly affected the O–H dissociation of FA as well as the CO2 adsorption capacity of the catalyst, which ultimately boosted the catalytic activity for both reactions. This work also represents a demonstration of a catalyst that promotes the reversible interconversion between FA and CO2 under heterogeneous conditions and is recyclable for at least three cycles without loss of activity. Additionally, the present catalyst performs well even in flow chemistry experiments using a fixed-bed reactor, indicating the potential for various industrial applications.

The hydrogen isotope deuterium is widely used in the synthesis of isotopically-labeled compounds and in the fabrication of semiconductors and optical fibers. However, the facile production of deuterium gas (D2) and hydrogen deuteride (HD) in a controlled manner is a challenging task, and rational heterogeneously-catalyzed protocols are still lacking. Herein, we demonstrate the selective production of hydrogen isotope compounds from a combination of formic acid and D2O, through cooperative action by a PdAg nanocatalyst on a silica substrate whose surface is modified with amine groups. In this process, D2 is predominantly evolved by the assist of weakly basic amine moieties, while nanocatalyst particles in the vicinity of strongly basic amine groups promote the preferential formation of HD. Kinetic data and calculations based on semi-classically corrected transition state theory coupled with density functional theory suggest that quantum tunneling dominates the hydrogen/deuterium exchange reaction over the metallic PdAg surfaces.

Formic acid (FA; HCOOH) is one of the most promising candidates for the storage of hydrogen (H2). Herein, we report a H2 storage/production system based on the hydrogenation of CO2 and dehydrogenation of FA, using a nanostructured heterogeneous catalyst. Pd1Ag2 nanoparticles with an average size of 2.8 nm were encapsulated within a zeolitic imidazolate framework (ZIF-8) having a core-shell structure (ZIF-8@Pd1Ag2@ZIF-8). This composite displayed high activity and stability during both the hydrogenation of CO2 to produce FA and the dehydrogenation of FA into H2 and CO2. This improved performance is attributed to the use of ultrafine Pd1Ag2 nanoparticles as well as the spatial regulation of the nanoparticles within the reaction field. This study suggests a new strategy for controlling the spatial distribution of metal nanoparticles within MOFs so as to fine-tune the catalytic activity and selectivity of ZIF-8@metal nanoparticles@ZIF-8 catalysts.

Pb-I layers in two-dimensional (2D) organic-inorganic hybrid perovskite thin films (CH3(CH2)3NH3)2(CH3NH3)Pb2I7 has been tried to preferentially orient perpendicular to substrates only by thermal annealing after spin coating of reagent solution for improvements of the energy-conversion-efficiency of solar cells. It is found from x-ray diffraction measurements that the ratio of diffraction intensity from (202) plane to that from (060) becomes larger in thermally annealed (50 – 135 oC) samples. This indicates that the Pb-I layer tend to grow perpendicular to the surface of the substrate. Especially, the ratio has reached to 8.2, which is larger compared with the ratio of 2.7 for randomly oriented powder sample, for the sample prepared on SnO2 substrates. Such (202) oriented films seem to contribute to improvements of the energy-conversion-efficiency of tandem type solar cells utilizing the 2D perovskite thin films as an active layer of the top cell.