Note: | Taiwan-France Collaborative Research Has Published Important Result on Water Catalysis
A collaborative research team of Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taiwan and University of Lille, France has just published a crucial result in Angewandte Chemie International Edition on the title of
Water Vapor Does Not Catalyze the Reaction between Methanol and OH Radicals
Recent works [Jara-Toro et al., Angew. Chem. Int. Ed. 2017, 56, 2166 and PCCP 2018, 20, 27885] suggested that the reactions of OH radicals with alcohols would become faster by up to 2 times at high humidity, suggesting that water molecules catalyze the reaction. If this was true, it would have an impact on the budget of alcohols in the atmosphere and might explain differences in measured and modeled methanol concentrations. However, the results were based on a relative technique carried out in a small Teflon bag, which might suffer from wall reactions. The Taiwan-France team has reinvestigated this effect using a direct fluorescence probe of OH radicals, and no catalytic effect of water could be found. This team also repeated the experiments in a Teflon bag, but was not able to reproduce the results of Jara-Toro et al. Further theoretical calculations show that the water-mediated reactions have negligible rates compared to the bare reaction and that even though water molecules can lower the barriers of reactions, it cannot make up for the entropy cost.
While scientists have been speculating for decades about the effect of water in a number of atmospheric reactions, reliable and clear evidence is quite sparse. This definitive work has set a constraint on the related chemical kinetics.
The idea of rechecking the water effect in the methanol + OH reaction was initially proposed by Dr. Jim Jr-Min Lin, a research fellow in IAMS, who discussed it with Dr. Christa Fittschen, a CNRS research director in University of Lille during a stay in Taiwan. They designed the necessary experiments, which were performed by Mr. Wen Chao, a research assistant in IAMS with laser induced fluorescence detection of OH radicals, during a visit in Lille using a facility constructed and supervised by Dr. Coralie Schoemaecker (ULille). Supplementary Teflon bag experiments were conducted by Dr. Alexandre Tomas (IMT Lille - Douai). Quantum chemistry and reaction rate calculation was done by Dr. Kaito Takahashi (IAMS).
This collaboration is a part of the Orchid program of Taiwan-France collaborative researches. The paper has been published in Angewandte Chemie, International Edition on February 21, 2019. [Wen Chao, Jim Jr-Min Lin, Kaito Takahashi, Alexandre Tomas, Lu Yu, Yoshizumi Kajii, Sébastien Batut, Coralie Schoemaecker and Christa Fittschen, Angew. Chem. Int. Ed. 2019, DOI: 10.1002/anie.201900711] |