High‐Surface‐Area TiO₂ and TiN as Catalysts for the CC Coupling of Alcohols and Ketones

Abstract

To design more sustainable processes for the alkylation of ketones, the use of both atom-ineffective leaving groups such as halides and boron as well as noble-metal-based catalysts should be avoided. For that purpose, high-surface-area titanium nitride was prepared from high-surface-area titanium dioxide using cyanamide as a transcription agent. The resulting nitride as well as the initial oxide proved to be effective and versatile catalysts for the alkylation of ketones with alcohols. Interestingly, the TiN catalyst yields unsaturated compounds, while the oxide-based catalyst mainly yields saturated coupling products. As a result of its metallic properties, TiN shows a strong tendency to catalyse the dehydrogenation of alcohols, which then undergo aldol condensation with ketones. In contrast, TiO(2) promotes the direct nucleophilic attack of ketones on alcohols.

Mesoporous, 2D Hexagonal Carbon Nitride and Titanium Nitride/Carbon Composites

“…Similar results were observed for mesoporous TiN [24] and TiN nanoparticles [41] synthesized with carbon nitride (or else cyanamide) as the nitrogen source. While there is a certain C 3 N 4 /Ti ratio needed to convert the oxide into the nitride, higher ratios always produce a certain amount of residual carbon.…”

“…As it exhibits enhanced hardness, TiN can be used, for example, for abrasives and hard coatings. [20,21] Furthermore, the application of TiN as electrodes for supercapacitors [22] and as a catalyst [23,24] has been reported, and titanium oxynitride has been applied as a photocatalyst. [25,26] Also for these applications, the control of the nanostructure of the metal nitride can have crucial influence on the performance; for example, high surface areas can increase electrode kinetics and catalyst activity.…”

“…Consequently, so far conversion of porous metal oxides into their corresponding metal nitrides has only been reported for substrate-supported materials in the form of porous thin films [26] or particulate, irregular porous materials. [24] Very recently, Zhao and coworkers were able to synthesize ordered mesoporous metal nitrides in the form of replicas from SBA-15 silica. [32] The synthesis of self-supported, ordered nanowire arrays was enabled by nitridation of metal oxides either before or after removal of the silica hard template.…”

Synthesis of Early‐Transition‐Metal Carbide and Nitride Nanoparticles through the Urea Route and Their Use as Alkylation Catalysts

“…[11] In addition, such a test proved very useful to determine which kind of reactions can be promoted by each type of particle. As well as the expected aklylation of ketones, we anticipated that other reactions could be observed such as the oxidation of benzyl alcohol, the formation of dibenzyl ether or the Friedel-Craftstype alkylation of the solvent (xylene).…”

“…To the best of our knowledge, only TiN found such applications, namely, for the selective hydrogenation of CÀC multiple bonds [10] or as a catalyst for the alkylation of ketones with alcohols (Scheme 1). [11] However, when the current financial crisis is over, the price of PGMs will surely increase again. This, in turn, will prompt intense efforts to substitute early-transition-metal ceramics (including oxides) [12,13] for noble metals, even in fine chemical synthesis.…”