The key activation step of the transformation of propan-2-ol, an abundantly available and inexpensive compound, into value-added fine chemicals catalyzed with super acids from two different families with heteroatom variations: heteropolyacids (H2SW12O40, H3PW12O40 and H4SiW12O40) and zeolites (H-[B]ZSM-5, H-[Al]ZSM-5 and H-[Ga]ZSM-5) and the result of the confinement effects were investigated by means of the density functional theory (M06-L) calculations [1-2]. The calculated deprotonation energies (kcal/mol) show the trend of acidity: H2SW12O40 (289.8) &gt; H3PW12O40 (291.4) &gt; H4SiW12O40 (295.5) &gt; H-[Al]ZSM-5 (319.9) &gt; H-[B]ZSM-5 (326.8) &gt; H-[Ga]ZSM-5 (349.4), which agrees with previous reports [3-5]. The adsorption of propan-2-ol over the POMs is found to be weaker than that over the zeoltic systems by about 5-10 kcal/mol, due mainly to the confinement effects provided by the zeolite framework. Under the influence of the zeolite framework in stabilizing cationic transition states, the dehydration of propan-2-ol over the MFI zeolites is expected to be better facilitated than the catalytic process over the heteropolyacids. However, the activation energy for the dehydration of propan-2-ol over the heteropolyacids is found to be lower than that on zeolites in accordance with the trend of acidity: H3PW12O40 (25.3) &gt; H2SW12O40 (27.9) &gt; H4SiW12O40 (29.2) &gt; H-[Ga]ZSM-5 (31.8) ≈ H-[Al]ZSM-5 (31.9) &gt; H-[B]ZSM-5 (34.7). Because of looser confinement, they inhibit the facile dehydration of the propan-2-ol, making these zeolytic materials much less reactive. The catalytic reactivity is controlled by the acidic strength of the catalyst and the specific stabilization of cationic transition states in the dehydration process.

Role of acid strengths and confinement effects on the conversion of propan-2-ol: MFI zeolites vs. Keggin polyoxometalates

249th National Meeting (2015)

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