Understanding the impact of water on the catalytic activity and stability

Inspired by my past work in solvent effects in organic reactivity, I have transferred the micro-solvation approach used in homogeneous phase to surface reactions aiming at understanding the role of water on the C-H and O-H scissions in alcohols [1]: H-bonded water strongly activates the O-H scission but does not affect the C-H scission on Rh. This discovery immediately questioned the role of water on the activity of other metals. I evidenced that the impact of water depends on the oxophilicity of the metal: the stronger the oxophilicity, the stronger the impact. My collaborator A. Ruppert confirmed this prediction experimentally on the levulinic acid conversion into gamma-valerolactone.[2] This collaborative work is an important milestone that put in evidence the importance of understanding the effect of water on the catalytic activity.

The pH also affects the catalytic activity: to proceed efficiently, alcohol oxidation by O2 using Au catalysts needs adding a base, which generates unwanted waste. Combining PCM and microsolvation, I included for the first time in a computational study the chemisorption of anionic hydroxide at the catalyst/water interface. Rationalizing the role of the added base, I identified potential sources of improvement to guide the Catalysis community: the basic pH polarizes the metal surface and a similar effect can be achieved through alloying, additives and support effect.[3]

Water is detrimental to the stability of gamma-Al2O3, a widely-used support in metal-supported catalysts. Using ab initio metadynamics combined with experiments, I proposed a mechanism of a reaction of a surface in contact with water, mapped out the weak spots of gamma-Al2O3 and proposed a rational for the protection offered by the adsorption of polyols.[4] This is one of the first examples of using this advanced simulation method to explore reactions at the solid/liquid interface.

References

  1. “C-H versus O-H Bond Dissociation for Alcohols on a Rh(111) Surface: A Strong Assistance from Hydrogen Bonded Neighbors”
    C. Michel, F. Auneau, F. Delbecq, and P. Sautet, ACS Catal. 2011, 1, 1430.
  2. “Role of water on metal catalyst performance for ketone hydrogenation. A join experimental and theoretical study on levulinic acid conversion into gamma-valerolactone,” C. Michel, J. Zaffran, A. M. Ruppert, J. Matras-Michalska, M. Jedrzejczyk, J. Grams, P. Sautet
    Chem. Comm. 2014, 50, 12450
  3. “Unraveling the Role of Base and Catalyst Polarization in Alcohol Oxidation on Au and Pt in Water »
    Gu, P. Sautet, and C. Michel, ACS Catal. 2018, 8, 11716.
  4. “Reactivity of shape-controlled crystals and metadynamics simulations locate the weak spots of alumina in water »
    Réocreux, E. Girel, P. Clabaut, A. Tuel, M. Besson, A. Chaumonnot, A. Cabiac, P. Sautet, C. Michel, Nat. Comm. 2019, 10, 3139