Novel nanoporous N-doped carbon-supported ultrasmall Pd nanoparticles: Efficient catalysts for hydrogen storage and release

Abstract

The reversible reactions involving formate and bicarbonate can be used to store and release hydrogen (H 2), allowing H 2 to serve as an effective energy carrier in energy systems such as fuel cells. However, to feasibly utilize these reactions for renewable energy applications, efficient catalysts that can reversibly promote both reactions are required. Herein we report the synthesis of novel polyaniline (PANI)derived mesoporous carbon-supported Pd nanoparticles, or materials that can efficiently catalyze these reversible reactions. The synthesis involves pyrolysis of PANI/colloidal silica composite materials at temperatures above 500 °C and then removal of the colloidal silica from the carbonized products with an alkaline solution. The resulting nanomaterials efficiently catalyze the reversible reactions, i.e., the dehydrogenation of formate (HCO 2 ‾ + H 2 O  H 2 + HCO 3 ‾) and the hydrogenation of bicarbonate (H 2 + HCO 3 ‾ H 2 O + HCO 2 ‾). The porosity and the catalytic property of the materials can be tailored, or improved, by changing the synthetic conditions (in particular, the pyrolysis temperature and the amount of colloidal silica used for making the materials). The study further reveals that having an optimum density of N dopant species in the catalysts makes Pd to exhibit high catalytic activity toward both reactions. Among the different materials studied here, the one synthesized at 800 °C with relatively high amount of colloidal silica templates gives the best catalytic activity, with a turnover frequency (TOF) of 2,562 h-1 for the dehydrogenation reaction and a turnover number (TON) of 1,625 for the hydrogenation reaction. These TOF and TON values are currently among the highest values reported for heterogeneous catalysts for these reversible reactions.

Cobalt Entrapped in N,S‐Codoped Porous Carbon: Catalysts for Transfer Hydrogenation with Formic Acid

“…[13] Among them, FA is almosta ni deal candidate for CTH because of its nontoxicity, convenience, and recyclability. [14,15] Unfortunately,m any of the reportede fficient catalysts for CTH generally necessitate the use of noble metals, [9,[16][17][18][19][20] seriously limiting the large-scale applications owing to the highe conomic cost and low availability.…”

Pyridinic Nitrogen‐Doped Graphene Nanoshells Boost the Catalytic Efficiency of Palladium Nanoparticles for the N‐Allylation Reaction

“…[27,28] For instance, Bi et al reported that pyridinic Nd oped carbon supports can enhance the catalytic performance of palladium for dehydrogenation of formic acid. [30] Nevertheless, no research hasf ocusedo na dvanced nitrogen-doped carbon-supported palladium catalysts towards N-allylation reactions.A dditionally,t he effect of the nitrogen-doped support, especially the nitrogen type, still requires furthere xploration and discussion. [30] Nevertheless, no research hasf ocusedo na dvanced nitrogen-doped carbon-supported palladium catalysts towards N-allylation reactions.A dditionally,t he effect of the nitrogen-doped support, especially the nitrogen type, still requires furthere xploration and discussion.…”

CO2‐Mediated H2 Storage‐Release with Nanostructured Catalysts: Recent Progresses, Challenges, and Perspectives

“…This condition is, however, less preferable as it requires high temperature and inert carrier gases, making the process expensive and less desirable. [57] Various multimetallic alloy nanoparticles possessing transition metals have recently been reported to catalyze FA dehydrogenation reaction in gas and solution phases. [43a,53] Recently, some researchers have also considered ionic liquids as reaction media to take advantage of the unique properties of ionic liquids to catalyze the reactions.…”

“…[80] For example, Pd nanoparticles supported on reduced graphene oxide (Pd NPs/r-GO) were reported to catalyze the dehydrogenation of formate with a TOF of 11 299 h −1 and the hydrogenation of bicarbonate with a TON of 7088 at 80 °C. [57] The catalytic activities of the material was improved by adjusting the structures and compositions of the support materials as well as the size of the Pd nanoparticles and the electronic properties around nanoparticles through the heteroatom dopants on the support material. Our group has also recently reported that heterogeneous catalysts comprising ultrasmall Pd nanoparticles supported on polymer-derived N-doped carbon (Pd/PDMC) catalyzed the dehydrogenation of formate with a TOF of 2562 h −1 and the hydrogenation of bicarbonate with a TON of 1625.…”

“…[57] After characterizing the catalyst by by X-ray photoemission spectroscopy (XPS), Raman spectroscopy and extended X-ray absorption fine structure (EXAFS)/near-extended X-ray absorption fine structure (NEXAFS), different isotopic labeling experiments were conducted using deuterated/nondeuterated formate and water, namely, i) D-CO 2 − + H 2 O (Reaction (1)), ii) H-CO 2 − + D 2 O (Reaction (2)), and iii) D-CO 2 − + D 2 O (Reaction (3)) (see Figure 16). In one of the few studies, performed by us, the reaction mechanisms for the dehydrogenation of NaHCO 2 and the hydrogenation of the product, NaHCO 3 , in aqueous solutions over Pd/PDMC catalyst have been reported.…”