Exploring the interaction between two neighbouring monomers has great potential to significantly raise the performance and deepen the mechanistic understanding of heterogeneous catalysis. Herein, we demonstrate that the synergetic interaction between neighbouring Pt monomers on MoS greatly enhanced the CO hydrogenation catalytic activity and reduced the activation energy relative to isolated monomers. Neighbouring Pt monomers were achieved by increasing the Pt mass loading up to 7.5% while maintaining the atomic dispersion of Pt. Mechanistic studies reveal that neighbouring Pt monomers not only worked in synergy to vary the reaction barrier, but also underwent distinct reaction paths compared with isolated monomers. Isolated Pt monomers favour the conversion of CO into methanol without the formation of formic acid, whereas CO is hydrogenated stepwise into formic acid and methanol for neighbouring Pt monomers. The discovery of the synergetic interaction between neighbouring monomers may create a new path for manipulating catalytic properties.
The low-temperature C−H bond activation of alkanes remains a big challenge in alkane dehydrogenation. In this work, ethylbenzene (EB) oxidative dehydrogenation has been investigated on rutile(R)-TiO 2 (110) under both ultrahigh vacuum (UHV) and ambient conditions. Under UHV conditions, styrene is produced with nearly 100% selectivity in a stepwise manner, in which the first C−H bond dissociation of EB occurs at <285 K with the help of surface O 2 2− species, followed by the second C−H bond dissociation at about 400 K. However, styrene, acetophenone, and 2,3-diphenylbutane products are produced from EB oxidative dehydrogenation under ambient conditions, suggesting that α-H dissociation is the initial step of EB oxidative dehydrogenation. This may be also possible for EB oxidative dehydrogenation on R-TiO 2 (110) under UHV conditions. The different pathways of EB oxidative dehydrogenation under UHV and ambient conditions may originate from different intermediates and O 2 concentrations. This work provides new insight into the fundamental understandings of the low-temperature C−H bond activation of alkyl chains of aromatic hydrocarbons, which may promote the development of new catalysts for efficient styrene production from EB oxidative dehydrogenation under mild conditions.
Direct functionalization of methane remains a key challenge, especially for using non-noble metal catalysts. We demonstrated that TiO 2 nanorods with abundant oxygen vacancies enabled mild oxidation of methane by H 2 O 2 into formaldehyde (HCHO) without light irradiation. The activity of TiO 2 nanorods with the concentration gradient of oxygen vacancies (V O ) increased with the V O concentration. In H 2 O 2 aqueous solution under 30 bar of CH 4 at 70 °C for 1 h, the TiO 2 nanorods with the most abundant V O exhibited a total oxygenate yield of 40.80 μmol, among which the selectivity for HCHO was 64.1%. On the basis of the catalytic and spectroscopic data, we identified the reaction intermediates and accordingly mapped the reaction scheme. Specifically, H 2 O 2 is activated on Ti atoms near V O to form surface peroxo intermediates, followed by the activation of CH 4 to produce methoxy groups. The methoxy group can react either with water to form methanol or with hydroxyl radicals to form CH 3 OOH. Methanol is attacked by hydroxyl radicals and dehydrated to form •CH 2 OH that further reacts with hydroxyl radicals and is dehydrated to HCHO. CH 3 OOH directly undergoes dehydration to engender HCHO.
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