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Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-enhanced Raman Scattering.

van Schrojenstein Lantman EM, Gijzeman OL, Mank AJ, Weckhuysen BM - ChemCatChem (2014)

Bottom Line: Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface.As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol.A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands).

ABSTRACT

Heterogeneous catalysis is a surface phenomenon. Yet, though the catalysis itself takes place on surfaces, the reactants and products rapidly take the form of another physical state, as either a liquid or a gas. Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface. Surface-enhanced Raman spectroscopy is an ideal technique to probe these self-assembled monolayers as it gives molecular information in a measured volume limited to the surface. We show how surface-enhanced Raman spectroscopy can be used to determine the reaction kinetics of a two-dimensional reaction. As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol. A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

No MeSH data available.


a) Reaction steps in a typical heterogeneous catalytic reaction from A(g) to B(g) involve adsorption of reactants A onto the catalytic surface, a surface‐reaction yielding a reaction product B, and subsequent desorption of the reaction products into the gas environment. b) A photocatalytic surface reaction is studied. Novel with respect to part a is that only the surface‐reaction is monitored, as a function of irradiation at λ=532 nm (5× objective, NA 0.12). c) The reaction under study is the photoreduction of pNTP to either p‐aminothiophenol or DMAB. For dilution experiments, thiophenol is used as the 2 D equivalent to a solvent.
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fig1: a) Reaction steps in a typical heterogeneous catalytic reaction from A(g) to B(g) involve adsorption of reactants A onto the catalytic surface, a surface‐reaction yielding a reaction product B, and subsequent desorption of the reaction products into the gas environment. b) A photocatalytic surface reaction is studied. Novel with respect to part a is that only the surface‐reaction is monitored, as a function of irradiation at λ=532 nm (5× objective, NA 0.12). c) The reaction under study is the photoreduction of pNTP to either p‐aminothiophenol or DMAB. For dilution experiments, thiophenol is used as the 2 D equivalent to a solvent.

Mentions: A typical heterogeneous catalytic reaction at a surface involves three separate steps, as shown in Figure 1 a, whereas a reaction within a SAM follows 2 D reaction kinetics on the catalyst surface (Figure 1 b). One of the most described reactions in a SAM is the photocatalytic reduction of p‐nitrothiophenol (pNTP). A large discussion point is the interpretation of the reaction product SERS spectrum, which could indicate either p‐aminothiophenol (pATP)12 or p,p′‐dimercaptoazobenzene (DMAB)13 (see also Figure 1 c). The challenge in the identification of the reaction product through other characterization techniques is twofold: an extremely low number of molecules are converted during the reaction and these few molecules are chemically bound to the surface. The latest developments indicate that the oxidation of pATP to DMAB is possible through a simultaneous plasmonic activation of oxygen.14 This is further supported by a thorough theoretical study into the reaction pathway.15 Others are still convinced that the reduction product of pNTP is pATP, based on a deviation of the Raman spectrum of neat pATP owing to chemical enhancement.16


Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-enhanced Raman Scattering.

van Schrojenstein Lantman EM, Gijzeman OL, Mank AJ, Weckhuysen BM - ChemCatChem (2014)

a) Reaction steps in a typical heterogeneous catalytic reaction from A(g) to B(g) involve adsorption of reactants A onto the catalytic surface, a surface‐reaction yielding a reaction product B, and subsequent desorption of the reaction products into the gas environment. b) A photocatalytic surface reaction is studied. Novel with respect to part a is that only the surface‐reaction is monitored, as a function of irradiation at λ=532 nm (5× objective, NA 0.12). c) The reaction under study is the photoreduction of pNTP to either p‐aminothiophenol or DMAB. For dilution experiments, thiophenol is used as the 2 D equivalent to a solvent.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4834625&req=5

fig1: a) Reaction steps in a typical heterogeneous catalytic reaction from A(g) to B(g) involve adsorption of reactants A onto the catalytic surface, a surface‐reaction yielding a reaction product B, and subsequent desorption of the reaction products into the gas environment. b) A photocatalytic surface reaction is studied. Novel with respect to part a is that only the surface‐reaction is monitored, as a function of irradiation at λ=532 nm (5× objective, NA 0.12). c) The reaction under study is the photoreduction of pNTP to either p‐aminothiophenol or DMAB. For dilution experiments, thiophenol is used as the 2 D equivalent to a solvent.
Mentions: A typical heterogeneous catalytic reaction at a surface involves three separate steps, as shown in Figure 1 a, whereas a reaction within a SAM follows 2 D reaction kinetics on the catalyst surface (Figure 1 b). One of the most described reactions in a SAM is the photocatalytic reduction of p‐nitrothiophenol (pNTP). A large discussion point is the interpretation of the reaction product SERS spectrum, which could indicate either p‐aminothiophenol (pATP)12 or p,p′‐dimercaptoazobenzene (DMAB)13 (see also Figure 1 c). The challenge in the identification of the reaction product through other characterization techniques is twofold: an extremely low number of molecules are converted during the reaction and these few molecules are chemically bound to the surface. The latest developments indicate that the oxidation of pATP to DMAB is possible through a simultaneous plasmonic activation of oxygen.14 This is further supported by a thorough theoretical study into the reaction pathway.15 Others are still convinced that the reduction product of pNTP is pATP, based on a deviation of the Raman spectrum of neat pATP owing to chemical enhancement.16

Bottom Line: Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface.As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol.A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

View Article: PubMed Central - PubMed

Affiliation: Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht (The Netherlands).

ABSTRACT

Heterogeneous catalysis is a surface phenomenon. Yet, though the catalysis itself takes place on surfaces, the reactants and products rapidly take the form of another physical state, as either a liquid or a gas. Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the molecules involved do not leave the surface. Surface-enhanced Raman spectroscopy is an ideal technique to probe these self-assembled monolayers as it gives molecular information in a measured volume limited to the surface. We show how surface-enhanced Raman spectroscopy can be used to determine the reaction kinetics of a two-dimensional reaction. As a proof of principle, we study the photocatalytic reduction of p-nitrothiophenol. A study of the reaction rate and dilution effects leads to the conclusion that a dimerization must take place as one of the reaction steps.

No MeSH data available.