Engineering sodium‐decorated bifunctional Au‐Ti sites to boost molecular transfer for propene epoxidation with H₂ and O₂

Abstract

Regulating the microenvironment of active sites is crucial to boost the performance of direct propene epoxidation with H2 and O2. Herein, the enhanced surface transfer of H2O2 intermediates was first achieved by sodium‐decorated Au‐Ti bifunctional active sites. Combined with multi‐techniques (e.g., operando UV–vis–NIR system, DFT studies and quantitative model calculations), it is found that the sodium‐decorated silanols (Si‐ONa species) on the TS‐1 support enhance the formation of Ti‐OOH intermediates by restraining H2O2 decomposition. In addition, sodium‐decorated silanols improves the desorption of propylene oxide, suppressing its ring‐opening and formation for the carbonaceous deposits. Moreover, the sodium‐decorated Au nanoparticles with smaller diameter and higher electron density further strengthen O2 adsorption and boost the H2O2 formation. This work not only provides fundamental understandings on the microenvironment of Au‐Ti bifunctional catalysts but also sheds new light on enhancing the performance by boosting the surface molecular transfer.

Regulating the Coordination Mode of Ti Atoms in the Beta Zeolite Framework to Enhance the 1-Hexene Epoxidation

“…In Ti-beta catalysts, the abundance of open Ti­(OH)­(OSi) 3 sites facilitates the easy formation of Ti-η 1 (OOH) species (Ti-OOH/Ti ratio: 13.3) compared to other Ti species. This initiation takes place through the reaction between Ti–OH and H 2 O 2 , demonstrating a remarkably high H 2 O 2 average utilization efficiency of 98.29%. ,, These Ti-η 1 (OOH) species are recognized as the active intermediates in olefin epoxidation. , Subsequently, these active intermediates attack the double bond of 1-hexene via an oxygen atom, leading to the creation of a transition state with a lower apparent activation energy (14.44 kJ mol –1 ) and the subsequent formation of 1,2-epoxyhexane . Due to their ability to activate H 2 O 2 into Ti-η 1 (OOH) species and lower apparent activation energies, Ti­(OH)­(OSi) 3 sites exhibit superior performance in the epoxidation of 1-hexene.…”

“…This initiation takes place through the reaction between Ti−OH and H 2 O 2 , demonstrating a remarkably high H 2 O 2 average utilization efficiency of 98.29%. 33,67,68 These Ti-η 1 (OOH) species are recognized as the active intermediates in olefin epoxidation. 69,70 Subsequently, these active intermediates attack the double bond of 1-hexene via an oxygen atom, leading to the creation of a transition state with a lower apparent activation energy (14.44 kJ mol −1 ) and the subsequent formation of 1,2-epoxyhexane.…”

Controlling the SAPO-34 Particle Size to Enhance Reaction-Diffusion Behavior for Improving Catalytic Efficiency in the MTO Reaction

“…Then, the N 2 adsorption–desorption isotherms of deactivated catalysts (Figure S2) were tested to discriminate the main factor of catalyst deactivation, which may be caused by the pore blocking and/or acid sites’ coverage due to coke deposition. − According to the function about the real coke density, ρ coke was estimated and listed in Table . V na was determined by N 2 adsorption–desorption, which is the micropore volume of fresh SAPO-34 zeolites minus that of deactivated SAPO-34 zeolites.…”

Regeneration of a Spent TS-1 Zeolite Catalyst for Liquid-Phase Epoxidation of Propylene and H2O2

“…Their i.r. absorptions are characterized by a sharp intensive band beyond 3740 cm –1 , a broadened less intensive band centered around 3500 cm –1 , and a shoulder weak band in between the two, respectively. ,− All of these silanol groups are related to the surface hydrophilicity of TS-1 zeolite, while the H-bonded silanols in hydroxyl nests and internal terminal silanols are active in the Na + -exchange reactions and also contribute to the surface acidity of TS-1 zeolite. ,,,,− Generally speaking, the acidity of the surface hydroxyl group of TS-1 is quite weak. However, it is strong enough to promote the alcoholysis of PO and methanol during liquid-phase epoxidation of propylene. ,,,− The acid-catalyzed alcoholysis of PO with methanol is one of the key secondary reactions in the propylene epoxidation, which generally gives a ring-opening product consisting of relatively more 2-methodoxy-1 propanol and less 1-methodoxy-2 propanol.…”