Mechanistic Investigation of Heterogeneous Catalysis by Transient Infrared Methods

Abstract

This paper provides an overview of the use of various transient infrared methods to determine the role of infrared observable species in the mechanisms of the NO-CO reaction, heterogeneous ethylene hydroformylation, and photocatalytic oxidation of ethanol. The transient infrared methods with a judicious choice of ways in changing the concentration of reactants and their isotope counterparts produce responses, allowing (i) identification of the spectators, (ii) determination of active adsorbed species, and (iii) verification of kinetic models and their parameters. The method has also been recently extended to monitor infrared absorbance of photogenerated electrons during photocatalysis, correlating variation in the concentration of photogenerated electrons and adsorbed species. The specific discussion focuses on limitations of the approaches and the type of mechanistic information that can be obtained.

In situ/operando studies for the production of hydrogen through the water-gas shift on metal oxide catalysts

“…This behavior is consistent with that observed by Clausen et al in their pioneer in situ XRD study of the WGS on CuO/ZnO. 18 Recently, inverse model catalysts of CeO x nanoparticles supported over Au(111) 15,51 or Cu(111) 52 have shown high catalytic performance in the WGS reaction, up to the point that a CeO x /Cu(111) system is more active than Cu/CeO 2 (111) and Cu/ZnO(000 % 1) systems. 52 As shown in Scheme 2, the inverse CeO 2 /CuO-Cu catalyst exposes ceria nanoparticles to the reactants.…”

“…18 The disappearance of the CuO lines and the gradual appearance of the Cu(111) line are clearly observed. Concurrent with the increase in the intensity, the width of the Cu (111) line is found to decrease due to an increase in the Cu particle size. 18 The morphology of the reduced Cu/ZnO catalyst was examined using an ETEM.…”

“…4,7,[80][81][82][83][84][85][86][87] Studies with single crystals show important differences in the WGS process on extended surfaces of Cu and Pt. 61,62,64,88 The turnover frequency of Pt( 111) is initially five times greater than that observed on Cu (111), a typical benchmark for the WGS reaction, 61,62,64 but Pt (111) undergoes deactivation due to the deposition of carbon by the Boudouard reaction: 2CO(surf) -C(surf) + CO 2 (gas). 88 When depositing Pt on an oxide one must modify the chemical properties of the metal to enhance the rate of dissociation of water and improve the selectivity towards the WGS to prevent carbon deposition through the Boudouard reaction.…”

“…1A displays an image of high-resolution transmission-electron microscopy (HR-TEM) for a high-surface area Pt-Ru/CeO 2 catalyst. 32 One sees particles of a Pt-Ru alloy (1.5-3 nm in size) on top of a ceria support that mainly exhibits the (111) face of the oxide. In the case of Fig.…”

Grafting of Amines on Ethanol-Extracted SBA-15 for CO2 Adsorption

“…The argon flow was then switched to a 10%CO 2 -90%N 2 mixture at a flow rate of 60 mL/min to allow adsorption. According to the mass balance of CO 2 , the adsorption capacities could be determined as follows [23]: $q=\frac{Q\left(t_s-t_0\right)C_{in}}{22.4W}$ $t_s=true{\int }_0^t(1-\frac{C_{out}}{C_{in}}false)dt$ where t s is the mean residence time (s); t 0 is the residence time of the empty bed; C in and C out are the inlet and outlet CO 2 concentration, respectively; q is the equilibrium absorption capacity of CO 2 (mmol/g); t is the absorption time (s); Q is the volumetric feed flow rate (mL/s) at standard temperature and pressure (1 atm and 0 °C); and W is the weight of the adsorbent (g); t 0 is measured by using the inert gas [57]. …”