Highly Selective Conversion of CH₄ to High Value‐Added C₁ Oxygenates over Pd Loaded ZnTi‐LDH

Abstract

The selective oxidation of methane to high value‐added liquid oxygenated compounds under mild conditions is of great significance to promote the efficient utilization of the carbon source, but it also faces the dilemma of low activity and over‐oxidation. Here, ZnTi‐layered double hydroxides (LDH)‐A200 photocatalysts with Pd loading are prepared to achieve efficient oxidation of methane, with O2 as an oxidant under ambient condition. The highest generation rate of C1 liquid products (methanol and formaldehyde) reaches 4924.47 µmol g−1 h−1 with a selectivity close to 100% over 0.5Pd‐ZnTi‐LDH‐A200, which is 20 times higher than that of bare ZnTi‐LDH‐A200. The photochemical results show that the modified photocatalysts present much higher generation and separation efficiency of electron‐hole pairs. In situ X–ray photoelectron spectroscopy indicates that Pd nanoparticles are the hole acceptor, which is beneficial to charge separation in the photocatalysis. Furthermore, electron spinresonance spectroscopy and temperature–programmed–desorption analysis prove that Pd loading is helpful to the adsorption of methane and oxygen on the surface of ZnTi‐LDH‐A200, promoting the production of reactive oxygen species and activation of methane. All these factors work together to promote the efficient conversion of CH4 to high value‐added C1 oxygenates.

Selective Photocatalytic Oxidation of Methane to Methanol by Constructing a Rapid O2 Conversion Pathway over Au–Pd/ZnO

“…Worth noting is that Au and Pd are effective catalysts for O 2 activation and subsequent oxidation reactions, but it is challenging to accurately regulate the pathway of O 2 evolution using only monometallic catalyst. ,− For example, as an excellent electronic conductor, Au can promote the separation of photogenerated carriers for the O 2 reduction into *OOH and H 2 O 2 , but it has a limited ability to break O–O bond into *O and *OH. − In contrast, Pd exhibits strong adsorption on the O 2 , leading to the effective cleavage of the O–O bond. And *OOH or H 2 O 2 can be easily decomposed into *O and *OH on Pd, but the strong interaction between *O and Pd may result in surface poisoning. ,, Recently, Jiang et al found that the selective formation of ROS could be regulated by adjusting the size of active sites (i.e., single atoms or nanoparticles) on the Au/In 2 O 3 catalyst.…”

Interstitial Zinc Defects Enriched ZnO Tuning O2 Adsorption and Conversion Pathway for Superior Photocatalytic CH4 Oxygenation

“…Noble metal (Pt, Au, Ag, Pd) modified photocatalysts have been widely developed for the oxidation of CH 4 into liquid oxygenates in the oxygen atmosphere, − because noble metals can act as both O 2 adsorption centers and photogenerated electron capture sites for the enhancement of O 2 conversion into active oxygen species . However, O 2 is usually adsorbed in a lateral configuration on the metal nanoparticle surface, which leads to the difficulty in the release of the generated •OOH but rapidly cracks into •OH to cause the overoxidation reaction .…”

Single‐Atom Alloys Materials for CO2 and CH4 Catalytic Conversion

“…The utilization of light or electricity to drive CH 4 and CO 2 conversions not only constitutes an environmentally sustainable and mild approach but also holds the potential to significantly reduce the activation barriers in thermodynamics. To date, considerable endeavors have been devoted to catalysts design for CH 4 and CO 2 conversion, encompassing methodologies such as hybridization, [15,16] alloying, [17,18] single-atom materials, [19][20][21] and other innovative approaches. Up to now, constructing single atom sites is considered an effective strategy to improve the metal utilization efficiency of catalysts for CH 4 and CO 2 conversion because a noble metal is often needed.…”