In situ FTIR studies on the oxidation of isopropyl alcohol over SnO2 as a function of temperature up to 600 °C and a comparison to the analogous plasma-driven process

The Effect of Water on the 2-Propanol Oxidation Activity of Co-Substituted LaFe1- Cox O3 Perovskites

Perovskites are interesting oxidation catalysts due to their chemical flexibility enabling the tuning of several properties. In this work, we synthesized LaFe_1−xCo_xO₃ catalysts by co‐precipitation and thermal decomposition, characterized them thoroughly and studied their 2‐propanol oxidation activity under dry and wet conditions to bridge the knowledge gap between gas and liquid phase reactions. Transient tests showed a highly active, unstable low‐temperature (LT) reaction channel in conversion profiles and a stable, less‐active high‐temperature (HT) channel. Cobalt incorporation had a positive effect on the activity. The effect of water was negative on the LT channel, whereas the HT channel activity was boosted for x>0.15. The boost may originate from a slower deactivation rate of the Co³⁺ sites under wet conditions and a higher amount of hydroxide species on the surface comparing wet to dry feeds. Water addition resulted in a slower deactivation for Co‐rich catalysts and higher activity in the HT channel state.

TiO2 with controllable oxygen vacancies for efficient isopropanol degradation: photoactivity and reaction mechanism

Flame-synthesized TiO_2−x with controllable defects exhibits a remarkable photooxidation efficiency of gaseous isopropanol with the reaction mechanism investigated.

A Process Analytical Concept for In-Line FTIR Monitoring of Polysiloxane Formation

The chemical synthesis of polysiloxanes from monomeric starting materials involves a series of hydrolysis, condensation and modification reactions with complex monomeric and oligomeric reaction mixtures. Real-time monitoring and precise process control of the synthesis process is of great importance to ensure reproducible intermediates and products and can readily be performed by optical spectroscopy. In chemical reactions involving rapid and simultaneous functional group transformations and complex reaction mixtures, however, the spectroscopic signals are often ambiguous due to overlapping bands, shifting peaks and changing baselines. The univariate analysis of individual absorbance signals is hence often only of limited use. In contrast, batch modelling based on the multivariate analysis of the time course of principal components (PCs) derived from the reaction spectra provides a more efficient tool for real-time monitoring. In batch modelling, not only single absorbance bands are used but information over a broad range of wavelengths is extracted from the evolving spectral fingerprints and used for analysis. Thereby, process control can be based on numerous chemical and morphological changes taking place during synthesis. “Bad” (or abnormal) batches can quickly be distinguished from “normal” ones by comparing the respective reaction trajectories in real time. In this work, FTIR spectroscopy was combined with multivariate data analysis for the in-line process characterization and batch modelling of polysiloxane formation. The synthesis was conducted under different starting conditions using various reactant concentrations. The complex spectral information was evaluated using chemometrics (principal component analysis, PCA). Specific spectral features at different stages of the reaction were assigned to the corresponding reaction steps. Reaction trajectories were derived based on batch modelling using a wide range of wavelengths. Subsequently, complexity was reduced again to the most relevant absorbance signals in order to derive a concept for a low-cost process spectroscopic set-up which could be used for real-time process monitoring and reaction control.

Surface chemistry of 2-propanol and O2 mixtures on SnO2(110) studied with ambient-pressure x-ray photoelectron spectroscopy

Tin dioxide (SnO₂) has various applications due to its unique surface and electronic properties. These properties are strongly influenced by Sn oxidation states and associated defect chemistries. Recently, the oxidation of volatile organic compounds (VOCs) into less harmful molecules has been demonstrated using SnO₂ catalysts. A common VOC, 2-propanol (isopropyl alcohol, IPA), has been used as a model compound to better understand SnO₂ reaction kinetics. We have used ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to characterize the surface chemistry of IPA and O₂ mixtures on stoichiometric, unreconstructed SnO₂(110)-(1 × 1) surfaces. AP-XPS experiments were performed for IPA pressures ≤3 mbar, various IPA/O₂ ratios, and several reaction temperatures. These measurements allowed us to determine the chemical states of adsorbed species on SnO₂(110)-(1 × 1) under numerous experimental conditions. We found that both the IPA/O₂ ratio and sample temperature strongly influence reaction chemistries. AP-XPS valence-band spectra indicate that the surface was partially reduced from Sn⁴⁺ to Sn²⁺ during reactions with IPA. In situ mass spectrometry and gas-phase AP-XPS results indicate that the main reaction product was acetone under these conditions. For O₂ and IPA mixtures, the reaction kinetics substantially increased and the surface remained solely Sn⁴⁺. We believe that O₂ replenished surface oxygen vacancies and that SnO₂ bridging and in-plane oxygen are likely the active oxygen species. Moreover, addition of O₂ to the reaction results in a reduction in formation of acetone and an increase in formation of CO₂ and H₂O. Based on these studies, we have developed a reaction model that describes the catalytic oxidation of IPA on stoichiometric SnO₂(110)-(1 × 1) surfaces.

Formation of microns long thin wire networks with a controlled spatial distribution of elements

By controlling the spatial distribution of elements using a simple self-assembly process, the catalytic performance can be enhanced.

An in situ FTIR study of the plasma- and thermally-driven reaction of isopropyl alcohol at CeO2: evidence for a loose transition state involving Ce3+?

This paper reports on the thermally-driven and non-thermal plasma-driven reaction of IsoPropyl Alcohol (IPA) on ceria (CeO₂) with the aim to investigate the differences between plasma catalytic interactions and the analogous thermal reactions.