Maria Olea

Temporal analysis of products: basic principles, applications, and theory

This paper discusses a temporal analysis of products approach, which can be considered as an advanced kinetic strategy at the boundary between traditional applied kinetics and surface science. The basic principles, examples of application in heterogeneous catalysis and theoretical framework are discussed.

TAP study on CO oxidation on a highly active Au/Ti (OH)4* catalyst

The CO oxidation with O2 on an active Au/Ti(OH)4* catalyst has been studied using a TAP (temporal analysis of products) transient technique to gain insights into the CO oxidation mechanism. Taking advantage of the TAP system, we have tried to elucidate the controversial mechanism proposed for the CO oxidation on supported gold catalysts. Pump–probe experiments have been performed to determine the lifetime of surface reactive intermediates involved in the oxidation reaction. In a typical pump–probe experiment the catalyst is first charged with a reactant pulse from the pump valve and then interrogated with a different pulse from the probe valve. Varying the time between the pump and probe pulses gives information related to the lifetime of surface intermediates. The pump–probe experiments together with single-pulse experiments revealed that molecularly and irreversibly adsorbed oxygen contributed to the catalytic CO oxidation. When CO was a pump molecule, the CO2 yield was not influenced by the pump–probe time interval. This means that CO reversibly adsorbs on the surface with a lifetime long enough to react with oxygen. Moreover, the nature and role of oxygen species in the reaction have been examined in the TAP reactor using 18O2 transient experiments. The results revealed that oxygen passed over the catalyst without isotope scrambling and that the lattice oxygen atoms exchanged only with CO2 formed by the CO oxidation reaction.

Computational Fluid Dynamics in Microreactors Analysis and Design: Application to Catalytic Oxidation of Volatile Organic Compounds

This paper deals with the design of a suitable microreactor for the catalytic oxidation of volatile organic compounds (VOCs). There are a number of ways to release VOCs into the atmosphere, typically during processing of natural gas and handling petroleum products. As VOCs are harmful to our health, there is increased scientific interest in developing technologies for their destruction. Catalytic oxidation is one of them. Microreactors have showed higher efficiency than the conventional ones, mainly due to their large surface area to volume ratio and excellent heat and mass transfer properties. The design of a microreactor can be explored based on simulation results obtained by using computational fluid dynamics (CFD) package of COMSOL Multiphysics. The first design step, based on cold flow simulation, was the selection of the most suitable microreactor geometry and configuration. Four different geometries had been proposed and simulated to evaluate the fluid behaviour in the microchannels. One of them, Type A2, allowed the most uniform flow distribution in all channels, as assessed through relative standard deviation calculations. The second design step involved the investigation of the VOCs catalytic oxidation, using propane as model molecule, occurring in the microreactor with the geometry/configuration previously found. The proposed microreactor consists of eleven parallel channels of square cross-section, with 0.5 × 10 -3 m width, 0.5 × 10 -3 m height and 0.1 m length. The catalytic microreactor was simulated for temperatures between 563 K and 663 K and inlet flow velocities from 0.01 to 1.00 m·s -1 . The exit propane conversion increased rapidly with increasing temperature for a fixed inlet flow velocity. For a fixed temperature, the propane conversion increased as the inlet flow velocity decreased.

Preparation and structural characterisation of SBA-15 supported nickel catalysts via sol-gel nickel oxide coatings for dry reforming of methane

Supported nickel catalysts have been prepared by coating mesoporous silica with nickel oxide through a sol-gel coating technology, other than the conventional impregnation procedure. Sol-gel nickel oxide coatings were first synthesized using nickel nitrate and lactic acid as precursors and then, deposited on the support of mesoporous silica SBA-15. Various synthetic parameters, such as the nickel/lactic acid molar ratio for the synthesis of the sol-gel coatings and the nickel/SBA-15 ratio for the preparation of the catalysts, were investigated. Scanning electron microscopy and energy-dispersive X-ray analysis, X-ray diffraction, thermal analysis and attenuated total reflection fourier transform infrared spectroscopy were used to characterise the nickel oxide sol-gel coatings and the resulting supported catalysts. The catalytic activity was tested using the Catlab integrated system. Results showed that this sol-gel coating route produces uniform nickel oxide thin films and leads to a good distribution of the nickel oxide on the mesopore surface of SBA-15. Compared with the catalyst prepared by impregnation with nickel nitrate salt solutions, the catalysts prepared through the sol-gel coating route are superb in nickel loading and distribution. The mesostructure of the supported catalysts remain unchanged after calcinations at elevated temperatures. Moreover, their catalytic activity towards the dry reforming of methane reaction is higher at temperatures lower than 700°C.

An In-Situ XAS Study of the Structural Changes in a CuO-CeO2/Al2O3 Catalyst during Total Oxidation of Propane

A CuOx‐CeOx/Al2O3 catalyst was studied with in‐situ transmission Cu K XAS for the total oxidation of propane as model reaction for the catalytic elimination of volatile organic compounds. The local Cu structure was determined for the catalyst as such, after pre‐oxidation and after reduction with propane. The catalyst as such has a local CuO structure. No structural effect was observed upon heating in He up to 600°C or after pre‐oxidation at 150°C. A full reduction of the Cu2+ towards metallic Cu0 occurred, when propane was fed to the catalyst. The change in local Cu structure during propane reduction was followed with a time resolution of 1 min. The χ(k) scans appeared as linear combinations of start and end spectra, CuO and Cu structure, respectively. However, careful examination of the XANES edge spectra indicates the presence of a small amount of additional Cu1+ species.