FTIR reaction mechanism studies

TG-FTIR has become a quite popular, versatile, cost-effective and informative instrument for modern polymer analysts concerned with compositional analysis and degradation/ reaction mechanism studies. The growth rate of TG/FTIR instrumentation currently exceeds that of TG-MS. 

For the studied catechol methylation reaction the catalyst structure and surface properties can explain the catalytic behaviour As mentioned above, the reaction at 260-350°C has to be performed over the acid catalysts. Porchet et al. [2] have shown, by FTIR experiments, the strong adsorption of catechol on Lewis acid/basic sites of the Y-AI2O3 surface. These sites control the reaction mechanism. 

One example of the application of in situ FTIR to the study of the near-electrode region concerns the study of the electro-oxidation of ethylene glycol (EG) at a platinum electrode in base. This work clearly illustrates the relative ease with which the products of an electrochemical reaction can be detected and identified, and a mechanism deduced. 

Other aspects of FTIR spectroscopy have not yet been put into practice. One could study the kinetics, and in particular the build-up and decay of intermediate radicals. This latter aspect would provide useful information to determine the mechanism of the reaction being studied. 

Many surface analysis techniques have been applied in studies on the reaction mechanism of APTS with silica gel.15 In order to study the chemical structure and interactions of the surface compound, FTIR has been recognized as a very powerful tool.2 8-16-17 18... 

Fundamental reaction mechanisms of epoxy cure have been fully investigated in the literature with the work of Lee and Neville being the reference of choice [2]. Recent studies focusing on fundamental reactions of epoxy and various hardeners have been performed using NMR and NIR/FTIR methods in the works of many researchers [86-95]. Mechanisms and kinetics of various epoxy systems has been evaluated and tabulated by Mijovic et al. and others [96, 97]. 

The elucidation of the reaction mechanism of the SCR reaction has been carried out using a variety of techniques. Transient studies with isotopically (oxygen-18 and nitrogen-15) labeled molecules have been performed [86,90]. Spectroscopic studies of the working catalysts were performed by Went et al. [90] and Topsoe [91] using laser Raman spectroscopy and FTIR, respectively. 

Reaction Mechanism. To understand the size-dependent reactivity of palladium clusters on MgO surfaces in more detail, combined Fourier transform infrared (FTIR) and thermal desorption (TDS) studies were performed. The cluster model catalysts were first exposed to 1 Langmuir of CO at 90 K and subsequently to the same amount of NO. Upon linearly heating the model catalysts, the product molecules C02 and were detected by mass spectrometry as a function of the cluster size for Pd with n < 30. While for Pd4, the formation of C02 is negligible, Pdg and Pdso form C02 at 305 K or 145K and 300K, respectively (Fig. 1.97). 

Assuming co-reaction, the cure reaction of a mixture of bis(4-maleimido phenyl) methane and BACY was followed by FTIR [221]. The reaction kinetics, studied by DSC, suggested dependency of cure mechanism on blend composition. The apparent activation energy computed by the Prime method increased with BMI content. The rate maximum at a fractional conversion range of 0.32-0.33 indicated an autocatalytic nature of the reaction. The different pattern of activation energy with fractional conversion for two different blend compositions indicated non-identical cure mechanisms for the two compositions. The cyclot-rimerization of BACY occurred during the cure of a 1 2 molar ratio of BMI and BACY. Since activation parameters derived from DSC method are generally not consistent, and since the cyanate cure can be catalyzed by impurities present in BMI, which was not taken into consideration, the authors conclusions on the cure mechanism based on DSC kinetics can be erroneous. 

The objective of this investigation is to study the effect of the platinum support material in the lean reduction of NOx using propene as the reducing agent. For this reaction we describe differences in total activity and selectivity between platinum supported on three different materials with increasing acidity SiC, AI2O3 and ZSM-5. The activities of the catalysts are studied in flow reactors under both transient (temperature ramps) and stationary conditions. Adsorbed species on the surface of the catalysts are characterised using in-situ Fourier transformed infiured spectroscopy (FTIR). Different reaction mechanisms and the nature of adsorbed species are discussed. 

Surface reaction mechanisms based on evidence from in situ transmission FTIR studies, have been proposed for the destruction of methylene chloride and carbon tetrachloride over Co-Y loaded with CraOs [93]. The proposed reaction mechanism for methylene chloride destruction is shown in figure 9. 

Haruta and coworkers [1] have suggested that different reaction mechanisms may be operative at different temperatures for CO oxidation. Extrapolating their suggestion, it is possible that different mechanisms occur on different active sites. The discussion below will focus only on the mechanism applicable to reactions near room temperature. Several mechanisms have been proposed in the literature. They can be classified into two categories those that occur entirely on the Au particles and those that involve the support. Based on FTIR and TAP reactor studies, it is generally agreed that CO is adsorbed weakly and reversibly on Au particles [42,43,44]. However, there are many proposals for the subsequent steps of reaction. 

As was mentioned above, in 2007, it was shown that SWNT covalently functionalized with a polymer may be obtained by a bulk polymerization [33]. The reaction mechanisms that occur in the polymerization processes can be understood by Raman light scattering and FTIR spectroscopic studies, which prove the functionalization of CNTs both with monomers (e.g. N-vinyl carbazole (VK)) and polymer molecules (e.g. PVK) [33]. 

In situ FTIR spectroscopy has proved to be very useful for the investigation of the reaction mechanisms of electrochemical reactions and structural changes of substances involved in these reactions. Two different methods are used external reflection absorption spectroscopy and internal reflection spectroscopy. The application of these methods to the study of the electrochemical doping process of polypyrrole, and the comparison of the results are described in this contribution. 

The condensation grafting of polyethylenimine (PEI) onto poly(acrylamide-co-acryhc acid) (PAM-co-AA) was studied by FTIR spectroscopy. The reaction mechanism, which proceeded by a two-step reaction, involved the conversion of AA to acid chloride (AC) using thionyl chloride, followed by the condensation of AC onto PAM and with amine onto PEI to form the graft copolymer (125). 

A highly crosslinked epoxy resin was modified by reactive blending with bisphenol A polycarbonate. The bisphenol A polycarbonate was dissolved at high temperature in the uncured epoxy resin before the curing process. The physical and chemical interactions between the two components were studied by FTIR spectroscopy and the reaction mechanisms were discussed. FTIR isothermal measurements showed that the presence of polycarbonate did not affect the overall curing mechanism but decreased both the initial reaction rate and the final conversion of reactants. 13 refs. 

The temperature of calcination is the most sensitive parameter for the particles size. The details of reaction mechanism of BaTiOs formation from barium titanyl oxalate have been studied a lot by thermochemical methods (TGA, DTA), X-ray diffraction, gas chromatography analysis and infrared spectroscopy (FTIR). The decomposition of barium titanyl oxalate proceeds in four stages as it is shown in Fig. 5.16. 

Fourier transform infrared spectroscopy (FTIR) is a powerful technique to probe real-time adsorbed surface species (reactants, intermediates, products) and solution constituents due to selected molecular dipole bond vibrations induced by tuned incident radiation [100]. FTIR has been used to study the formic acid electrooxidation reaction mechanism in situ by stepping or scanning the potential where species of interest are generated, from either high potentials where the intermediate species are completely oxidized (a clean surface, >1 V vs. RHE) or low potentials where the intermediate species approaches the coverage limit (blocked surface, <0.05 V vs. RHE) [100]. The three observed reaction intermediates for formic acid electrooxidation are linearly bonded COl, bridge-bonded COb, and bridge-bonded formate (HCOOad) with vibrational bands at 2,052-2,080 cm 1,810-1,850 cm , and 1,320 cm , respectively [27, 98]. The vibration frequencies of the adsorbates are influenced by the electronic characteristics and electrochemical potential of the electrode surface. Additional peaks of lesser intensity are observed for the water adlayer and sulfate/bisulfate at the electrode interface [27, 98]. 

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