Covalently attached NH2 functional groups on SiO2 particles’ surface (H2N@SiO2), have been evaluated as cocatalyst for H2 production by the homogenous [RuIII /P(CH2CH2PPh2)3] catalyst using Formic Acid (FA) as substrate. It is found that the heterogeneous H2N@SiO2 cocatalyst (97μmoles ΝΗ2) is able to enhance dramatically the TONs of H2 production by &gt;700%, while the homogeneous amine NEt3 (97μmoles ΝΗ2) is inducing 350% enhancement in TONs. Based on a thermodynamic study for the two catalytic systems, we have estimated the activation energy barriers to be Ea=53 ±8 kJ/mol in the case of RuIII /P(CH2CH2PPh2)3/FA/NEt3, vs. Ea= 28 ±5 kJ/mol for RuIII /P(CH2CH2PPh2)3/FA/ H2N@SiO2. This shows that the H2N@SiO2 cocatalyst lowers the Ea of the process by almost 47%. We discuss a reaction mechanism where this Ea corresponds to the rate limiting-step which is the formation of bidentate HCOO- anion. The H2N@SiO2 cocatalyst could be reused 4 times with a &lt; 30% loss of activity after each reuse. TGA analysis and FT-IR data show that this loss of activity is correlated with a loss of the NH2-propyl-functionalities from the SiO2 particle i.e. after the 4th reuse practically all of the surface-grafted NH2-propyl-groups have been detached from the SiO2 particle. Finally, using EPR and UV-Vis spectroscopy, we show that the complete reduction of all RuIII centers to RuII oxidation state, are required for efficient H2 production. This RuIII reduction to RuII is triggered by bidentate coordination of formate resulting to rapidly formate decomposition via a [RuII-hydride] species. Based on these data, a self- consistent catalytic cycle is discussed.

NH2-based heterogeneous cocatalyst boosts H2-production from HCOOH by the RuIII /P(CH2CH2PPh2)3 catalyst

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.