Seite - 100 - in Advanced Chemical Kinetics

10−4 M (4–20 ppm) RuH2(N2)(PPh3)3, 1 M NaOH, and an intense light source at 150°C [5]. A mechanism as depicted in Figure 2 was proposed. In 2013, Beller disclosed a procedure for homogeneously catalysed aqueous-phase reforming type conversion of MeOH/H2O mixtures to 3H2 and CO2 (or other C1 residuals, such as carbon- ate, see Figure 7) [15]. Using 1.6 ppm of [RuHCl(PNPiPr)CO] in MeOH with 8.0 M KOH at 95.0°C afforded a TOF1h of 4719 h −1. Furthermore, using 19 ppm of [RuHCl(PNPPh)CO] with respect to MeOH in a 9:1 (v/v) MeOH/H2O mixture afforded a TOF1h of 63 h−1 at 65°C. As a note, the TOF was counted in such way that a complete reaction of MeOH/H2O mixtures to CO2 and 3H2 sums as three turnovers. This was done because all three reactions depicted in Figure 7 occurs simultaneously, rendering any quantitative kinetic discrimination between them unpractical. The system turned out to be very robust, with a TON over 350,000 and reaction time exceed- ing 23 days when using 1 ppm catalyst loading with respect to MeOH of [RuHCl(PNPiPr) CO] in a refluxing 9:1 (v/v) MeOH/H2O solution containing 8.0 M KOH. Moreover, after the 23 days a 27% yield of full MeOH reforming was achieved (based on H2 evolution and yield based on H2O as the limiting factor. The yield is 12% with respect to MeOH). When using 150 ppm, a CO2-based yield of 43% was reached within 24 h (yield based on H2O as the limit- ing factor. The yield is 19% with respect to MeOH). It was also demonstrated that a continuous production of a 3:1 H2/CO2 gas mixture, and hence full MeOH reforming, can be achieved by employing 250 ppm catalyst loading with respect to MeOH of the [RuHCl(PNPPh)CO] in a refluxing 4:1 (v/v) MeOH/H2O solution containing 0.1 M NaOH. After an initiation time of approximately 5–6 h, the expected 3:1 ratio of H2 and CO2 was observed in the gas mixture. In addition, the pH dropped from 13 to approximately 10 during the first 4 h. It was suggested that during this initiation time, the hydroxide was reacting with formic acid and CO2 leading to an eventual equilibrium between hydroxide/(bi) carbonate/formate as the C1 residuals. The catalyst activity was depending on a range of factors. Besides the reaction temperature the pH, base additive, and catalyst loading all influenced the activity. As such, a higher pH and lower catalyst loading promoted an increased turnover frequency. The latter is in agreement Figure 7. Aqueous MeOH AAD to 3H2 and C1 residuals by Beller. Best results: TOF = 4719 h−1. TON > 350,000. Yield = 43%. Stable for more than 23 days. Advanced Chemical Kinetics100