Production of H2 by Photocatalysis of H2O using Fe and Co Porphyrins and Corroles

MIGUEL MORALES; VALENTÍN AMOREBIETA; NICOLÁS I. NEUMAN; FABIO DOCTOROVICH

Huatulco

Congreso; International Conference on Polymers and Advanced Materials, ?POLYMAT?/ Simposio Latinoamericano de Química de Coordinación y Organometálica ?SILQCOM? 2013; 2013

POLYMAT - SILQCOM - Universidad Nacional Autónoma de México

Production of H2 by Photocatalysis of H2O using Fe and Co Porphyrins and Corroles Miguel A. Morales Vásqueza, Valentín Amorebietab, Nicolas Neumana and Fabio Doctorovicha* aDepartamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria, Pabellón II, Buenos Aires (C1428EHA), Argentina. * e-mail: mmorales@qi.fcen.uba.ar, Fax: 54-11-4576-3341, ext. 223 bGrupo de Química Inorgánica, Facultad de Ciencias Exactas y Naturales Universidad Nacional de Mar del Plata, Dean Funes 3350, Mar del Plata (B7602AYL), Argentina. ABSTRACT The Fe and Co corroles shown in Figure 1 were synthesized using the method of A. D. Alder's and Grycko, T et al. [1,2]. Commercially available metalloporphyrines were also tested. Photocatalytic hydrogen production in a mixture of THF/water in the presence of the abovementioned compounds and a series of irreversible electron donors such as triethylamine (TEA) and p-terphenyl (TP) have shown excellent activity in the production of hydrogen and high catalytic ability. This was achieved by reducing metalloporphyrins and metalocorrols by UV irradiation: in some cases these processes are MIIIP ? MIIP and in others MIIP ? MIP, as shown in the UV-Vis spectra shown in Figure 2. Such metalloporphyrines and metallocorroles already reduced were used as catalytic agents for the formation of hydrogen (H2) by reduction of water. The viability of this reaction in water seems to be very promising, shown by the formation of 0.54 atm hydrogen pressure (Figure 3), which is observed in the presence of water (blue line). To complete its catalytic cycle, the same catalyst is activated again (reduction by UV lamp in the presence of TEA) and it is observed that this produces a little more hydrogen (red line), but to a lesser extent, since most of it has degraded due to the photoreduction. In this case the TON (turnover number) was 252 and the TOF (turnover frequency) 8,4 min-1. Hydrogen gas has been detected by mass spectrometry using for example THF as solvent, with added H2O or D2O. Other signals observed were considered to be due to the vapors of THF and TEA. To ensure this result it was compared with the mass spectrum of a similar assay conditions but without porphyrin (blank), which shows no mass = 2. Photoreduction is efficient for MIIIP ? MIIP, and probably occurs by intramolecular electron transfer from an axially coordinated TEA. However, TEA does not bind to reduced metal complexes, and the quantum efficiency is much lower for the subsequent reduction steps.[3] Catalytic performances are significantly incremented by the addition of p-terphenyl (TP) as a sensitizer. The TP is fotoreduced very effectively by TEA to form the radical anion, TP?-, which has a reduction potential negative enough to reduce CoIIP and FeIIIP and quickly achieve CoIP and FeIIP status. The results show that TP improves the catalysts employed, as shown in Figure 4. In the presence of TP the TON was 218000 and the TOF 9083 min-1, being both of them around a thousand times larger than in the presence of TEA alone, which shows a huge improvement in the activity of the catalysts. BIBLIOGRAPHY [1] A. D. Alder; F. R. Longo and J. D. Finarelli, J. Org. Chem.; 1967, 32, 476 [2] Beata Koszarna and Daniel T. Gryko; J. Org. Chem.; 2006, 71, 3707 [3] T. Dhanasekaran, J. Grodkowski, and P. Neta; J. Phys. Chem. A; 1999,103, 7742