Towards an understanding of the beneficial effect of mesoporous materials on the dehydrogenation characteristics of NH3BH3

Abstract

Ammonia borane (AB) was loaded onto a range of mesoporous materials (MCM-41, SBA-15 and MCF) by wet impregnation from THF solutions and its thermal dehydrogenation studied using TGA/MS. The interactions between the AB and the surfaces were characterised using difference FTIR spectroscopy. The presence of mesoporous materials promotes lower temperature H 2 release, and greater selectivity towards the formation of H 2 , i.e. decreased formation of gaseous boroncontaining side products. D-FTIR results confirm interactions between isolated silanol groups or surface Si-O-Si species and AB and this supports the proposal that a H-bonding interaction between the surface and deposited AB is important in promoting decomposition at lower temperature. AB interacting with silanol groups decomposes more readily than that coordinated to Si-O-Si. The effect on the temperature of H 2 release is greater for materials of larger pore size (rather than materials of larger surface area), i.e. MCF>SBA-15>MCM-41. This suggests that access to the internal surface of the mesoporous material (where the majority of surface silanols are located) is important, and this in turn suggests that polymeric species, which may have restricted access to the internal surface of the different materials, form when AB is dissolved in THF. Decomposition of B-N-containing gaseous materials (to AB(g)) following their formation, on the silanol groups of the SiO 2 , is suggested as the reason for the increased selectivity of the reaction to H 2 (and decreased release of unwanted side products) in the presence of mesoporous material.

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

“…In addition, the Pd-Rh@PVP nanoparticle's catalyst maintained 78% of initial catalytic activity in AB hydrolysis, even after the fifth reaction. Because of its high hydrogen production activity in transition metal catalysts, platinum has attracted widespread attention [80,81], and been deeply studied by scholars. Kinetic studies and model calculations [57] show that Pt (111) facets are the main active surface.…”

“…Porous Pt25Pd75 NPs with a Pd-on-Pt structure could better combine with the B atom in AB to activate the electronic B-H bond, making it easier to break the attack with H2O [89]. Due to its high specific Because of its high hydrogen production activity in transition metal catalysts, platinum has attracted widespread attention [80,81], and been deeply studied by scholars. Kinetic studies and model calculations [57] show that Pt (111) facets are the main active surface.…”

Ammonia Borane Nanospheres for Hydrogen Storage

“…AB in the pristine state is however not suitable for solid-state hydrogen storage because of inappropriate dehydrogenation features. , Destabilization strategies have thus been developed in order to decrease the onset dehydrogenation temperature (<100 °C) while avoiding decomposition of AB into unwanted byproducts like borazine. The destabilization approaches reported to date are as follows: solubilization of AB in a solvent with or without a homogeneous dehydrocoupling catalyst; − addition of a solid-state doping agent; − insertion of AB into the porosity of a scaffold (i.e., nanoconfinement); − and chemical modification toward synthesis of alkali amidoborane derivatives MNH 2 BH 3 (M = Li, Na, K). , …”

Carbon supported bimetallic Ru-Co catalysts for H2 production through NaBH4 and NH3 BH3 hydrolysis

“…The use of heterogeneous catalysts allows an easy control of the H 2 generation rate just by acting on the flow of the hydride solution through the catalyst, making these systems more appropriate for hydrogen on demand applications. 22,23 The stability of AB at pH 7 is of practical importance as it allows the use of a larger number of supports, as silica, ceria, and zeolites, [24][25][26] not suitable under the strongly basic pH conditions of the SB solution. 11 Most used supports in NaBH 4 hydrolysis were activated carbon, 9,11,19 alumina, 20 and ion exchange resins.…”

“…21 More recently, ammonia borane (NH 3 BH 3 , coded AB) was accounted an interesting alternative to SB, exhibiting higher H 2 capacity (19.6 wt%) together with a low toxicity and a high stability in ambient conditions. 22,23 The stability of AB at pH 7 is of practical importance as it allows the use of a larger number of supports, as silica, ceria, and zeolites, [24][25][26] not suitable under the strongly basic pH conditions of the SB solution. Several catalysts have been found effective in accelerating NH 3 BH 3 hydrolysis (NH 3 BH 3 + 2H 2 O → NH 4 BO 2 + 3H 2 ), namely, noble metals, 27,28 nonnoble metals, 29,30 and B-containing nanocomposites.…”