Elizabeth Rojas

Tuning of Active Sites in NiNbO Catalysts for the Direct Conversion of Ethane to Acetonitrile or Ethylene

NiO nanoparticles that are highly active for the ethane activation have been prepared. These nanoparticles have been dispersed on the surface of two different Nb2O5 materials by using a novel dry nanodispersion method. This article describes the characterization and catalytic behavior of both series of catalysts as well as the nature of the active sites required for the transformation of ethane into acetonitrile and/or ethylene. It is demonstrated how such active sites present in the catalysts are obtained through this novel dry mixing method. The catalysts obtained are promising catalytic materials for both, ethane ammoxidation and oxidative dehydration (ODH) reactions.

In situ Raman studies during sulfidation, and operando Raman-GC during ammoxidation reaction using nickel-containing catalysts: a valuable tool to identify the transformations of catalytic species

Ni-containing catalysts are investigated under reaction conditions for two different cases, during sulfidation, with Ni-Mo based catalysts, and during ammoxidation reaction, with the Ni-Nb catalysts. It is shown how Raman spectroscopy can follow some of the transformations of these catalysts upon different treatments. For the NiMo/Al(2)O(3)-SiO(2) system it was possible to identify some of the sulfided Mo species formed during the sulfidation of the oxide precursors, while for the bulk Ni-Nb oxide catalysts the simultaneous reaction-Raman results strongly suggest that the incipient interaction between niobium and nickel oxides at low Nb/Ni atomic ratios is directly related to catalytic activity, and that a larger size well-defined NiNb(2)O(6) mixed oxide phase is not active for this reaction. Moreover, the promotion by niobium doping appears to be limited to a moderate niobium loading. It was found that in situ and operando Raman are valuable techniques that allowed the identification of active Mo-S and Ni-Nb species under reaction conditions, and that are not stable under air atmospheres.

Niobia-Supported Nanoscaled Bulk-NiO Catalysts for the Ammoxidation of Ethane into Acetonitrile

Two series of supported nanoscaled NiO catalysts have been prepared using Nb2O5 supports with different surface areas. NiO nanoparticles interacting with Ni–O–Nb mixed phases are active and selective for ethane ammoxidation; both are required in order to have an active and selective catalyst. In this paper we report the dispersion of NiO nanoparticles on two Nb2O5 supports in order to generate an active phase for ethane ammoxidation. The use of a support stabilizes NiO nanoparticles, which otherwise would sinter. This work shows how the activity can be modulated by the size of the NiO nanoparticles and by the NiO/Ni–Nb–O ratio, which depends on the nickel coverage and support surface area. The catalysts obtained are very promising for ethane ammoxidation reaction.Graphical Abstract

Performance of NiO and Ni–Nb–O active phases during the ethane ammoxidation into acetonitrile

There is a need to develop catalysts for the direct ammoxidation of ethane to acetonitrile. This work reports a series of bulk Ni–Nb–O catalysts with increasing niobium content, analysing the structure and the effect on acidity and redox properties and how these relate to Ni–Nb interaction. Niobium doping affects NiO lattice leading to progressively smaller unit cell sizes. The Nb/Ni atomic ratio determines the formation of two Nb–Ni–O mixed phases identified by HRTEM, and which Raman bands are identified near 850 cm−1 and 800 cm−1 for a Nb-poor phase and near 800 cm−1 for a Nb-rich Ni–Nb–O one.

Niobiosilica Materials as Attractive Supports for Sb–V–O Catalysts

Since niobium species have been described as being able to increase the catalytic properties of the Sb–V–O catalytic system, the main objective of the present paper is to design a non ordered-mesoporous Nb-containing material useful to be used as a support for this kind of catalysts. Such a material has been used as support for Sb–V–O active phases and the catalysts have been characterized and tested for the propane ammoxidation reaction. For comparative purposes, and in order to evaluate the role of niobium species, the study has been also performed with a support without niobium. The results have shown how the incorporation of niobium species into the support matrix with the procedure described here leads to the formation of a very promising catalytic support. The Nb species incorporated into the support cooperate with vanadium species of the SbVOx active phase increasing its performance for nitrile insertion into propane. Since Nb is a common additive that improves the catalytic behavior of different catalytic systems, the mesoporous Nb-containing support described in the present paper could be useful for other catalysts and/or catalytic processes.