dc.contributor.author	Schwartz, Viviane	en
dc.contributor.committeechair	Oyama, Shigeo Ted	en
dc.contributor.committeemember	Velander, William H.	en
dc.contributor.committeemember	Deck, Paul A.	en
dc.contributor.committeemember	Gibbs, Gerald V.	en
dc.contributor.committeemember	Cox, David F.	en
dc.contributor.department	Chemical Engineering	en
dc.date.accessioned	2014-03-14T20:08:00Z	en
dc.date.adate	2000-03-11	en
dc.date.available	2014-03-14T20:08:00Z	en
dc.date.issued	2000-03-02	en
dc.date.rdate	2001-03-11	en
dc.date.sdate	2000-03-06	en
dc.description.abstract	A series of niobium-containing nitride and carbides were prepared by a temperature-programmed synthesis method. The catalysts synthesized comprised a monometallic niobium oxynitride and a new bimetallic oxycarbide supported system, Nb-Mo-O-C/Al₂O₃ (Mo/Nb = 1.2; 1.6; 2.0). In the case of the niobium oxynitride, the progress of formation was analyzed by interrupting the synthesis at various stages. The effect of the heating rate on product properties was also investigated. The solid intermediates and the final niobium oxynitride were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (CHNS), and gas adsorption techniques. The solid state transformation occurred directly from Nb₂O₅ to NbN<sub>x</sub>O<sub>y</sub> without any suboxide intermediates. The bimetallic supported oxycarbide materials were also characterized by X-ray diffraction (XRD), gas adsorption techniques, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS). It was found that the electronic properties of the oxycarbide were modified by the interaction with the Al₂O₃ support, and that most of the oxygen atoms were associated with the niobium rather than the molybdenum atom. All of the niobium-containing catalysts were tested in a three-phase trickle-bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene. The niobium oxynitride presented low HDS activity and moderate HDN activity, whereas the supported bimetallic oxycarbide was found to be highly active for both, HDN and HDS, demonstrating higher activities than the commercial sulfided Ni-Mo/Al₂O₃ when compared on the basis of active sites. In addition to these studies a comprehensive investigation of the HDN reaction mechanism was carried out over bulk unsupported Mo₂C, NbC, NbMo₂-O-C, and compared with the mechanism over a sulfide catalyst, MoS₂/SiO₂. For this purpose, a comparison of the HDN rate of a series of isomeric amines was performed, and the reaction occurred mainly through a β-elimination mechanism for all catalysts. Temperature programmed desorption of ethylamine was used to investigate the acid properties of the catalytic surfaces, and a good agreement between the specific rate of reaction and the number of Brønsted acid-sites was obtained. Infrared spectroscopy showed that the amines interacted with acidic centers to form adsorbed quartenary ammonium species. The deamination reaction over the carbide and sulfide catalysts probably occurs by a concerted push-pull mechanism involving basic sulfur species and Brønsted-acidic centers. In order to obtain more insight into the mechanism a study of the pyridine HDN network was carried out.All of the catalysts showed the same activity trend: the reactivity of n-pentylamine was high, while those of piperidine and pyridine were relatively low. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio (r = k₂/k₁) between the rate constants of the two consecutive reactions, hydrogenation of pyridine (k₁) and ring opening of piperidine (k₂). The order of activity of the carbides and sulfide differed considerably depending on the substrate. However, for the pyridine reaction network the similarity in product distribution suggested that a similar surface composition, a carbosulfide, was attained during the reaction.	en
dc.description.degree	Ph. D.	en
dc.identifier.other	etd-03062000-21090032	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-03062000-21090032/	en
dc.identifier.uri	http://hdl.handle.net/10919/26368	en
dc.language.iso	en	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	chapter3_a.pdf	en
dc.relation.haspart	chapter5.pdf	en
dc.relation.haspart	listfigs.pdf	en
dc.relation.haspart	chapter3_b.pdf	en
dc.relation.haspart	chapter1.pdf	en
dc.relation.haspart	vita.pdf	en
dc.relation.haspart	chapter6.pdf	en
dc.relation.haspart	chapter4.pdf	en
dc.relation.haspart	tablconten.pdf	en
dc.relation.haspart	chapter2_a.pdf	en
dc.relation.haspart	titlepg.pdf	en
dc.relation.haspart	abst.pdf	en
dc.relation.haspart	chapter4_a.pdf	en
dc.relation.haspart	chapter3.pdf	en
dc.relation.haspart	chapter2.pdf	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	hydrodenitrogenation mechanism	en
dc.subject	niobium nitride	en
dc.subject	bimetallic carbide	en
dc.title	Preparation and Reactivity of Niobium-Containing Hydrotreating Catalysts	en
dc.type	Dissertation	en
thesis.degree.discipline	Chemical Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en

Preparation and Reactivity of Niobium-Containing Hydrotreating Catalysts

Files

Original bundle

Collections