Selective Grafting of Ga(i-Bu)₃ on the Silanols of Mesoporous H-ZSM-5 by Surface Organometallic Chemistry

Abstract

The reaction of triisobutylgallium toward meso-H-ZSM-5250, prepared by desilication of H-ZSM-5, has been studied by IR, high field solid-state NMR, and EXAFS spectroscopies as well as elemental analysis. Grafting occurs selectively on silanol groups, resulting in the monopodal gallium species [(≡SiO)­Ga­(i-Bu)2]. Since the Brønsted acidic protons remain largely unreacted, control of the surface organometallic chemistry affords a zeolitic material with both gallium sites and significant Brønsted acidity. The resulting bifunctional Ga­(i-Bu)3/meso-H-ZSM-5250 shows higher activity and selectivity in propane aromatization than monofunctional meso-H-ZSM-5250. The aromatic products arise from alkane dehydrogenation on the gallium sites, followed by oligomerization, cyclization, and aromatization of the resulting olefins on the Brønsted acid sites.

Bifunctional Catalysts Based on Tungsten Hydrides Supported on Silicated Alumina for the Direct Production of 2,3‐Dimethylbutenes and Neohexene from Isobutene

“…Twop eaks are identifieda td = 0.2 and 1.8 ppm, assigned to HO-m 1 -Al and HOÀSi, respectively.I na ddition, the signal at d = 1.8 ppm displayed as houlder at d = 4ppm that corresponds typicallyt oS i À(OH)Al as in zeolite. [36] Conversely,n op eak at d = 7ppm (relatedt os trongB rønsted acid)w as observed in agreement with previous studies in whichaprobe molecule (TMPO,t rimethylphosphineo xide)w as used to highlight this signal. [37] The intensities of the aluminolp eaks decreased with the increase of the silica content.They remained observablei nherently in the form of shouldersa round the silanol peaks for Siral 10-500 and disappeared entirely for the supports( Siral x-500 )i n which the amount of silica is greater than or equal to 20 wt %.…”

Olefin Oligomerization by Main Group Ga3+ and Zn2+ Single Site Catalysts

“…23,24,27,28 These structures differ from organometallic catalysts where metal alkyls, like trimethylgallium, were grafted to a SiO 2 support resulting in M-M bonds. [29][30][31] The rates and selectivities of single site Ga/SiO 2 and Zn/SiO 2 for propylene hydrogenation and propane dehydrogenation are similar to those previously reported (Table S2,S3). 24,32 Taken together, the XAS structures and catalytic performance con rm that single site, main group Zn 2+ and Ga 3+ silica supported catalysts have been prepared in agreement to previous literature.…”

Multi‐electron Reduction Capacity and Multiple Binding Pockets in Metal–Organic Redox Assembly at Surfaces

“…Surfaces upported single-site metal centers have begun to generatei nterest for applications in heterogeneous catalysis with the goal of high product selectivity.T his active research field includes severals trategies to achieves ingle-site centers (SSCs):s ingle atom alloys, [1] selectiveg rafting, [2] and 1D metalligand coordination networks. [3] Our work focuses on metal-organic coordinations trategies through on-surface redoxa ssembly of metal-organic complexes.T he uniformity of active sites in theses ystems allows for reactivity analogous to that of molecular catalysts while maintaining the practical benefits of traditional heterogenousc atalysts.…”

“…Surface supported single‐site metal centers have begun to generate interest for applications in heterogeneous catalysis with the goal of high product selectivity. This active research field includes several strategies to achieve single‐site centers (SSCs): single atom alloys, selective grafting, and 1D metal–ligand coordination networks . Our work focuses on metal–organic coordination strategies through on‐surface redox assembly of metal–organic complexes.…”