The detection of intermediate species formed during surface chemical reactions is essential because it can provide critical information about the reaction mechanisms at surfaces and interfaces. Therefore, the overarching goal of this research was to understand the mechanisms of surface catalytic, photocatalytic, and photoinduced reactions by monitoring the intermediate species formed during these reactions. To understand the initial steps of the carbon monoxide hydrogenation reaction on two-dimensional (2D) MoS2 and TaS2 materials, temperature programmed desorption and reaction are employed. Large-area 2D-MoS2 and 2D-TaS2 were prepared on a Cu(111) substrate under ultra-high vacuum conditions via physical vapor deposition. The highly crystalline surfaces of both 2D MoS2 and 2D TaS2 exhibited poor catalytic properties. However, when defects are created at the surface, the catalytic activity of these materials dramatically increases. The CO hydrogenation reaction on both surfaces proceeds through the dissociative adsorption of H2 and the formation of HCO. HCO is directly detected from TaS2, but not from MoS2, because of the ability of MoS2 to break the C-O bond of HCO monomers and dimmers, which leads to the detection of C2H2. To study the mechanisms of photoinduced and photocatalytic reactions, a technique based on time-of-flight mass spectrometry in conjunction with femtosecond pump-probe spectroscopy is employed. In one example, the photoinduced reaction of CD3I on an amorphous cerium oxide surface is studied with time, mass, and energy resolution to understand the effect of surface morphology on the reaction dynamics. In a different example, the photocatalytic water (D2O) splitting in the presence of CH3I on a TiO2(110) surface is studied. Rich details about the reaction mechanism are obtained through the detection of intermediates such as D, OD, DO2, CH3, and I, and final products such as CH3D and CH3OD. This type of research could open new avenues for understanding a variety of heterogeneous chemical reactions.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Pathan, Md Afjal Khan, "Understanding the Mechanisms of Surface Chemical Reactions by Tracking Unstable Intermediate Species" (2021). Electronic Theses and Dissertations, 2020-. 1150.