“…It is well-known that the rate of catalytic hydration is found to be of first order in the propylene concentration and protonic acid (H S + ) concentration on the catalytic surface. , Therefore, the rate of catalytic hydration becomes proportional to K w , which is the ion product of the bulk phase water raised to the 0.45th power. The result agrees with our experimental observation that the rate is proportional to K w raised to the 0.4th power.…”
We investigated the detailed mechanism of the relationship between the H+ concentration in
the bulk phase and the activity of protonic acid sites on the catalytic surface. The theory clearly
shows that the acidity of the catalytic surface is strongly affected by the change of the ion product
in the bulk phase water. This phenomenon was apparent with other kinds of metal oxide catalysts
and is largely caused by the change in the surface charge of the catalyst. In fact, through the
kinetic analysis of the catalytic hydration of propylene with a TiO2 catalyst in sub- and
supercritical water, the reaction rate of the hydration could be expressed as a function of both
the reaction temperature and ion product of water.
“…It is well-known that the rate of catalytic hydration is found to be of first order in the propylene concentration and protonic acid (H S + ) concentration on the catalytic surface. , Therefore, the rate of catalytic hydration becomes proportional to K w , which is the ion product of the bulk phase water raised to the 0.45th power. The result agrees with our experimental observation that the rate is proportional to K w raised to the 0.4th power.…”
We investigated the detailed mechanism of the relationship between the H+ concentration in
the bulk phase and the activity of protonic acid sites on the catalytic surface. The theory clearly
shows that the acidity of the catalytic surface is strongly affected by the change of the ion product
in the bulk phase water. This phenomenon was apparent with other kinds of metal oxide catalysts
and is largely caused by the change in the surface charge of the catalyst. In fact, through the
kinetic analysis of the catalytic hydration of propylene with a TiO2 catalyst in sub- and
supercritical water, the reaction rate of the hydration could be expressed as a function of both
the reaction temperature and ion product of water.
“…When one of the mechanisms of the gas-phase catalytic reactions is consulted, the kinetic description of the propylene hydration rate is obtained by applying Langmuir−Hinshelwood (LH) kinetics where two reactants are competing with each other for the adsorption sites as eq 1, − where K P and K H are the adsorption equilibrium constants of propylene and water, respectively, k is the specific rate constant on the surface, and the reaction is assumed to be first order on the adsorbed propylene and water concentration individually. Because of the high concentration of water, we assume that The simplified LH rate equation is where …”
Section: Resultsmentioning
confidence: 99%
“…According to the previous researchers, , the rate of catalytic hydration is proportional to the concentrations of propylene and protonic acid on the surface of the catalyst, though no information on the effect of the H + concentration in the bulk phase on the reaction rate is available. The present finding that the reaction rate of heterogeneous catalysis in supercritical water depends on the ion product of water implies that the H + concentration in the bulk phase is related to the number and/or activity of protonic acid sites on the catalyst surface, though the detailed mechanism is left to future studies.…”
We carried out a catalytic hydration of propylene with MoO 3 /Al 2 O 3 in sub-and supercritical water. MoO 3 /Al 2 O 3 catalyst promoted hydration of propylene to form 2-propanol as a sole product and exhibited stronger activity than Al 2 O 3 , which is known to function as an acid catalyst. It was also experimentally found that the reaction temperature near the critical temperature of water gave a maximum conversion of propylene. The rate of this catalytic hydration could be expressed as a function of both the reaction temperature and the ion product of water, implying that the catalytic activity of the acid sites in MoO 3 /Al 2 O 3 is strongly affected by the concentration of H + in the bulk phase.
“…As a side reaction, oligomers can also be formed through the addition of another propene molecule rather than water. Kinetically, the hydration of propene over HZSM-5 zeolites may follow a Langmuir−Hinshelwood mechanism. , 1 Possible Reaction Pathways in the Hydration of Propene…”
Catalytic attempts as well as thermodynamic considerations were employed to explore possible measures for
enhancing the yield of 1-propanol in propene hydration. The cost of 1-propanol production may be largely
reduced if it can be produced from the direct hydration of propene. The thermodynamic considerations suggest
that equilibrium distribution of 1- and 2-propanol depends almost solely on reaction temperature; the selectivity
of 1-propanol increases linearly with the temperature. Catalytic tests over zeolites HNU-3 and HZSM-5 prove
that the reaction behavior is related to the pore structure and surface acidity of zeolites, which could be
adjusted through modification with SiCl4 or NH4F. Modification of zeolites may suppress the formation of
byproduct oligomers, but has only limited improvement on 1-propanol yield. Strong acidity of zeolites is
favorable for the hydration to approach the reaction equilibrium, and therefore enhances the selectivity of
1-propanol.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
