Study of surface acid–base properties of natural clays and zeolites by the conversion of 2-methylbut-3-yn-2-ol

Abstract Surface acid–base properties of natural clays and non-clay minerals from Jordanian (J) and Russian (R) deposits as well as H-ZSM-5 were studied applying catalytic reaction of 2-methylbut-3-yn-2-ol (MBOH) conversion. Products of both acidic and basic pathways of the reaction were formed involving surface acid/basic sites of clay minerals. Specific conversions of MBOH decreased in the following order: kaolinite-R > hydromica-R > bentonite-J > red-kaolinite-J = palygorskite-R = H-ZSM-5 > zeolite-J > white-kaolinite-J > diatomite-J, which fairly correlated with TPD-NH3 acidity assessment for a majority of samples. However, a contribution of basic sites to the reaction should be taken into account, especially for hydromica-R and kaolinite-R. The strength of acid sites of natural aluminosilicates was compared based on surface acidity and reaction product yields. After 116 min of MBOH conversion, the strength of acid sites changed in the following order: kaolinite-R > palygorskite-R > bentonite-J > red- kaolinite-J > white-kaolinite-J > zeolite-J > diatomite-J > H-ZSM-5. At an early (17 min) stage of the reaction, the strength of active sites for natural zeolite-J and H-ZSM-5 were comparable, while the latter underwent significant deactivation due to its microporous structure. The rise of activation temperature from 500 °C to 700 °C for montmorillonite containing sample increased the conversion of MBOH due to the formation of stronger or additional number of basic sites as a result of mineral dehydroxylation. Natural clay samples with a higher content of montmorillonite (30–80%) altered the acid–base properties of the surface and observed higher ability to convert MBOH over acid and basic pathways.