Formic Acid Dehydrogenation via an Active Ruthenium Pincer Catalyst Immobilized on Tetra-Coordinated Aluminum Hydride Species Supported on Fibrous Silica Nanospheres

Abstract

The demand for harmless and efficient energy sources is remarkably expanding, particularly after the increased awareness of global warming, greenhouse gas emissions, immense fossil fuel consumption, and so forth. Formic acid is considered a potential candidate as an energy carrier for reversible hydrogen storage owing to its decomposition to hydrogen (H2) and carbon dioxide (CO2) in the presence of suitable catalysts. However, selective and efficient decomposition of formic acid using classical heterogeneous catalysis is still challenging because most heterogeneous catalysts which are known are ill defined. Herein, we report a promising heterogeneous approach toward formic acid dehydrogenation using a ruthenium PN3P pincer complex, [Ru–H(CO) ( tBuPN3P)] (I), immobilized on a fibrous silica nanosphere, KCC-1, with a strong Lewis acid character [(Si–O–Si) (Si–O−)2Al–H]. The resulting heterogeneous catalyst, [Ru(H) (CO) (tBuPN3P)]@[(Si–O–Si) (Si–O−)2Al–H] (III), has been fully characterized by advanced solid-state characterization techniques. In this compound, Al is tetrahedrally coordinated. It is a single-site catalyst which exhibits good stability toward water, high pressures, and high temperatures as well as good activity in formic acid dehydrogenation. An excellent turnover number of 600,000 and a recyclability of up to 45 cycles are observed.

Iridium Catalyst Immobilized on Crosslinked Polyethyleneimine for Continuous Hydrogen Production Using Formic Acid

“…In contrast, in the case of mixed conditions with homogeneous catalyst 1 and PEI, the TOF decreased to 29 000 h À 1 , implying a negative effect of PEI on the homogenous catalyst 1. However, the TOF of Cp*Ir@PEI remains high (73 200 h À 1 at 90 °C in water with 7 M formic acid, Figure S16) as compared to those for other types of immobilized catalysts on silica (TOF = 11 200 h À 1 , 24 000 h À 1 , 35 000 h À 1 in DMSO at 90 °C) [14,15,16] or that on polymer (TOF = 4,060 h À 1 ). [10d] The stability of the Cp*Ir@PEI catalyst was evaluated via repeated addition of 2.26 mL neat formic acid seven times without the catalyst separation.…”

Selective and controlled H2 generation upon additive-free HCOOH dehydrogenation over a Pd/NCS nanocatalyst

“…Since 1978, 33 formic acid (HCOOH), which could be readily obtained from biomass, has been deemed as the most promising liquid hydrogen carrier due to its excellent hydrogen storage capacity (4.4 wt% and 53 g L −1 ), low toxicity, outstanding stability and safe transportation/storage. [34][35][36][37][38][39][40] As a consequence, plenty of heterogeneous and homogeneous catalysts have been explored for selective H 2 evolution from formic acid dehydrogenation (HCOOH → H 2 ↑ + CO 2 ↑) and preventing CO release from formic acid dehydration (HCOOH → H 2 O + CO↑). [41][42][43][44][45][46][47] superior catalytic activities in H 2 generation from formic acid dehydrogenation because the alloying of Ag could enrich the electron cloud density of the Pd atom in PdAg, which was in favor of C-H bond cleavage in HCOOH dehydrogenation.…”

High-pressure hydrogen generation from dehydrogenation of formic acid

“…13–21 This has drawn the attention of many researchers and several very active homogeneous as well as heterogeneous catalysts have been developed over the past 15 years which efficiently dehydrogenate FA to H 2 and CO 2 selectively. 22–50 In this context, iridium based catalytic systems were found to be most effective. For instance, in 2015, Li et al developed a Cp*-Ir( iii ) catalyst containing a bisimidazoline ligand ( 1 in Fig.…”

“…1) to efficiently catalyze FADH with a TON of 600 000 and recyclability of up to 45 cycles. 49 Recently, Nielsen et al explored Ru-PNP complexes ( 10 in Fig. 1) in combination with an ionic liquid (1-ethyl-3-methylimidazolium acetate, EMIM OAc) for FADH, achieving an overall TON exceeding 18 million.…”