Nanotubular OMS-2 Supported Single-Atom Platinum Catalysts Highly Active for Benzene Oxidation

Abstract

The cryptomelane-type octahedral molecular sieve (OMS-2) exhibits excellent catalytic activity for the oxidation of volatile organic compounds (VOCs) due to its unique structure, and single-atom catalysts (SACs) have recently attracted much attention in heterogeneous catalysis. Herein, we adopted the hydrothermal redox reaction of KMnO4 and HCl aqueous solution at 120 °C for 12 h to first synthesize the nanotubular OMS-2 support and used the vitamin C and NaBH4 reduction methods to prepare the OMS-2-supported single-atom Pt and PtNP catalysts for benzene oxidation, respectively. It was found that the OMS-2-supported single-atom Pt catalyst with a Pt loading of 0.0383 wt % (0.0383Pt1/OMS-2) exhibited the best catalytic performance for benzene oxidation (a 90% benzene conversion was achieved at 189 °C and 20 000 mL g–1 h–1 (space velocity)), which was associated with its high surface oxygen vacancy density, good low-temperature reducibility, and strong benzene adsorption ability. It was also shown that benzene could be dissociated more readily over the supported single-atom Pt1 catalyst than over the supported PtNP catalyst, and the phenolates or benzoquinone as well as methyl groups, lipid, and vinyl species were the main intermediates in the oxidation of benzene over 0.0383Pt1/OMS-2. The results of this study are useful in developing the high-performance single-atom catalysts that can be applied for the oxidative removal of VOCs.

Noble Metal Single‐Atom Catalysts for the Catalytic Oxidation of Volatile Organic Compounds

“…Based on the above discussion, it is concluded that the application of metal SACs for highly efficient oxidation of VOCs is still in its infancy and most catalysts studied have been oxide‐supported noble metals. To guide the future study of metal SACs in the catalytic oxidation of VOCs, we therefore provide our insights on this emerging research area below: (1) Several metal SACs have shown better activity than nanocatalysts in the oxidation of several VOCs, such as Ag 1 /HMO, [12a] Pt 1 /OMS‐2 [12b] and Pt 1 /meso‐Fe 2 O 3 [13] SACs in benzene oxidation and a Pt 1 /TiO 2 SAC in C 2 H 4 /C 3 H 6 oxidation [12e] . However, there are several cases showing that the specific activity of the metal SAC is less than that of the nanocluster and nanoparticle.…”

“…OMS‐2 supported precious metal SACs, such as Pt [12b,13] and Pd [14b] SACs, have also been reported in catalytic benzene oxidation. For example, a nanotubular OMS‐2 supported Pt SAC (0.0383 wt% Pt 1 /OMS‐2) exhibited better catalytic activity ( T 50 =166 °C and T 90 =189 °C) toward benzene as compared to a Pt nanocatalyst (0.09 wt% Pt NP /OMS‐2, T 50 =189 °C and T 90 =206 °C) in benzene oxidation [12b] . Moreover, the performance of the Pt 1 /OMS‐2 SAC was better than that of the other SACs (Table 1) in benzene oxidation.…”

“…The presence of water vapor in the reaction can cause the deactivation of metal SAC [12b,d,13,14,28b,53] . For a Pt 1 /Co 3 O 4 SAC, water inhibited the catalytic activity in methanol oxidation [12d] .…”

“…For a Pt 1 /Co 3 O 4 SAC, water inhibited the catalytic activity in methanol oxidation [12d] . Adding 1–5 vol % of H 2 O into the gas feed (C 6 H 6 /O 2 ), the K/Ag 1 ‐OMS‐40 [14a] and Pt 1 /OMS‐2 [12b] catalysts presented lowered C 6 H 6 conversion. This was because water molecules occupied the active sites and adsorption centers.…”

“…Indeed, several SACs have been developed to oxidize VOCs and have shown better performance than nanocatalysts [12] . For example, Ag 1 /HMO, [12a] Pt 1 /OMS‐2 [12b] and Pt 1 /meso‐Fe 2 O 3 [13] SACs are more efficient than their counterpart nanocatalysts in benzene oxidation. In C 2 H 4 /C 3 H 6 oxidation, a Pt 1 /TiO 2 SAC is more active than a Pt NP /TiO 2 nanocatalyst [12e] .…”