Measurements of the wettability of catalyst support materials using the Washburn capillary rise technique

• Wetting of selected catalyst support materials was probed with organic solvents.
• Solvent choice for heterogeneous reactions is rationalised by this method.
• Polar aprotic solvents generally showed the fastest wetting rates.
• Moderately polar solvents like ethyl acetate or dioxane show the greatest versatility.
• Results are discussed in terms of the surface chemistry of the supports.

The penetration of porous solids by organic solvents is a technologically important phenomenon, relevant to a wide variety of fields including heterogeneous catalysis. Selecting the most appropriate solvent is a critical, albeit sometimes overlooked, step in such processes. In this study, the Washburn capillary rise technique was used to determine the wetting rates and contact angles of fifteen different organic solvents on some typical catalyst support materials, with the aim of better reaction design. This technique relates the rate at which a solvent is imbibed vertically through a bed of powder to the contact angle of the analyte solvent on the powder's surface. Experiments conducted on a range of catalyst support types indicated that contact angles were consistently low on silica and alumina supports regardless of the nature of the imbibed solvent, but were significantly higher on hydroxyapatite and microcrystalline cellulose-type supports. Oven drying of the powders only induced statistically significant changes in the wetting behaviour of some systems. The solvents with the most consistent wetting properties were those with moderate polarity such as tetrahydrofuran or ethyl acetate, making them the most versatile group of solvents for reactions involving the tested powdered supports.

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