A. Goguet

ABSTRACT In the preparation of silica-supported nickel oxide from nickel nitrate impregnation and drying, the replacement of the traditional air calcination step by a thermal treatment in 1% NO/Ar prevents agglomeration, resulting in highly dispersed NiO. The mechanism by which NO prevents agglomeration was investigated by using combined in situ diffuse reflectance infrared fourier transform (DRIFT) spectroscopy and mass spectrometry (MS). After impregnation and drying, a supported nickel hydroxynitrate phase with composition Ni3(NO3)2(OH)4 had been formed. Comparison of the evolution of the decomposition gases during the thermal decomposition of Ni3(NO3)2(OH)4 in labeled and unlabeled NO and O2 revealed that NO scavenges oxygen radicals, forming NO2. The DRIFT spectra revealed that the surface speciation evolved differently in the presence of NO as compared with in O2 or Ar. It is proposed that oxygen scavenging by NO depletes the Ni3(NO3)2(OH)4 phase of nitrate groups, creating nucleation sites for the formation of NiO, which leads to very small (4 nm) NiO particles and prevents agglomeration.

ABSTRACT The partial substitution of Co by Ru in lanthanum cobaltite perovskites (LaCo1−xRuxO3, x = 0.05 and 0.2) and its influence on the reducibility and structural modifications in the perovskite lattice have been evaluated by N2 adsorption isotherms, in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Characterization of LaCo1−xRuxO3 perovskite precursors reveals that Ru is incorporated into the perovskite lattice, producing a distortion of the original rhombohedral structure, a decrease in mean crystallite size and some increase in the surface area. The structural evolution of the LaCo1−xRuxO3 precursors under a reductive treatment indicates that Ru promotes the reducibility of the perovskite leading to a greater reduction degree of cobalt species. Moreover, the smaller perovskite crystallites obtained with the partial substitution of cobalt by ruthenium evolve to smaller crystal domains of both Co0 and La2O3 after reduction. The catalysts formed after the reduction of perovskite precursors present very high catalytic efficiency to extract hydrogen from diesel molecules by oxidative reforming. However, those catalysts derived from Ru-substituted perovskites show better catalytic performance associated with the higher development of active metallic phases achieved on the surface of these catalysts. Additionally, Ru promotes the catalytic activity and stability for this reaction increasing the reduction degree of cobalt and decreasing coke formation and sulfur poisoning through the formation of smaller cobalt crystallites.

This paper discusses a number of checks that should be carried out to ensure that the kinetic and spectroscopic measurements made using a DRIFTS cell are meaningful. The observations reported here demonstrate how an appropriately modified commercial DRIFTS cell can provide pertinent kinetic information about both gaseous products and the related surface intermediates. The oxidation of CO with O2 was