Surface properties and catalytic activities of amorphous niobium phosphate and a comparison with those of H3PO4-treated niobium oxide

Niobic acid and niobium phosphate as highly acidic viable catalysts in aqueous medium: Fructose dehydration reaction

“…The Brønsted acidity of niobic acid is very high (H 0 À5.6), niobium phosphate has also acid properties (H 0 À8.2) with a higher ratio of Lewis/ Brønsted acid sites. The textural, acidic, and catalytic properties of NBP are superior to those of NBO, with the advantage that these properties are preserved at higher temperatures [6][7][8][9][10].…”

N-alkylation of aniline with ethanol over an industrial niobic acid catalyst ? influence of water formation on kinetics and selectivity

“…The catalyst is produced by H.C. Starck and applied e.g., by Bayer for the studied reaction. The 5 · 5 mm cylindrical pellets, containing graphite as inert additive, were crushed and sieved to a defined particle size (20)(21)(22)(23)(24)(25) in order to reduce inner particle diffusion limitation. The BET surface area, the pore volume and the average pore diameter were determined by nitrogen adsorption using a Micromeritics Gemini 2375 apparatus after evacuating the sample at 200°C for 2 h. The water content was determined by weight loss after high temperature treatment of the catalyst powder.…”

“…Moreover, the acidic property of niobic acid can be increased by treatment with sulfuric or phosphoric acid [19][20][21]. On the contrary to other metal oxides, niobic acid looses catalytic activity by heat treatment above 400-500°C [14,15,22] due to an irreversible dehydration and the formation of crystalline niobium pentoxide Nb 2 O 5 [22], which shows no surface acidity (table 1).…”

Cyclooctene epoxidation using Nb-MCM-41 and Ti-MCM-41 synthesized at room temperature

“…Catalysts containing niobium have recently been studied, but not many references can be found in the literature [5]. The most important reactions using niobium as catalyst are dimerization and oligomerization of ethene [6], oxidative dehydrogenation of ethane [7], alkylation of benzene [8], oxidation of methanol [9,10], dehydration and dehydrogenation of alcohols [11] and polycondensation of terephthalic acid with ethylene glycol [12]. The development of niobium chemistry for catalysis has economic importance for Brazil, as it holds approximately 90% of the world-wide reserves of this metal, and is responsible for 92.4% of all world-wide niobium compounds produced [13].…”