IR study of adsorption and reaction of methylbutynol on the surface of pure and modified MgO catalysts:: probing the catalyst surface basicity

FT infrared spectroscopy (FTIR spectroscopy) has been used to study the adsorption and reactivity of 2-methyl-3-butyn-2-ol (MBOH) on the Surfaces of pure and Cs+ - and Ba+ -modified MEG. It has been found that MBOH is adsorbed via two different mechanisms. Dissociative adsorption at acid-base (M-O) pair-sites with the creation of new H-bonded surface OHs groups is the most favorable adsorption mode in the case of Cs/MgO, This is attributed to the strong Lewis basic sites generated on the catalyst surface upon impregnation with Cs+ cations which facilitate abstraction of hydrogen from MBOH, leading to the formation of alcoholate species. On the other hand, the Ba/MgO catalyst adsorbs MBOH preferentially via interaction with surface hydroxyl groups. Both these adsorption modes are operative on the surface of pure MgO. The acetylenic group is also involved in the adsorption of MBOH. The acidic acetylenic hydrogen interacts with the Lewis basic sites, whereas the Lewis acid sites interact preferably with the acetylenic pi-electron system. With regard to surface reactivity,the catalysts are active towards the decomposition of MBOH to acetone and acetylene, revealing their basic properties. The Cs/MgO catalyst exhibits higher activity than MgO, which appears to be more active than catalysts impregnated with Ba2+ ion. The formation of BaCO3 las detected by X-ray diffractometry (XRD) on the MgO surface may be responsible for this lower activity. It has been found that the reaction product acetone is polymerized rapidly and adsorbed strongly on the surfaces of Ba/MgO, In conclusion, the basicity of this series of catalysts can be ranked as follows: Cs/MgO > MgO > Ba/MgO (C) 2000 Elsevier Science B.V. All rights reserved.