Transport Mediating Core-Shell Photocatalyst Architecture for Selective Alkane Oxidation

Steering Photooxidation of Methane to Formic Acid over A Priori Screened Supported Catalysts

Efficient methane photooxidation to formic acid (HCOOH) has emerged as a sustainable approach to simultaneously generate value-added chemicals and harness renewable energy. However, the persistent challenge lies in achieving a high yield and selectivity for HCOOH formation, primarily due to the complexities associated with modulating intermediate conversion and desorption after methane activation. In this study, we employ first-principles calculations as a comprehensive guiding tool and discover that by precisely controlling the O2 activation process on noble metal cocatalysts and the adsorption strength of carbon-containing intermediates on metal oxide supports, one can finely tune the selectivity of methane photooxidation products. Specifically, a bifunctional catalyst comprising Pd nanoparticles and monoclinic WO3 (Pd/WO3) would possess optimal O2 activation kinetics and an intermediate oxidation/desorption barrier, thereby promoting HCOOH formation. As evidenced by experiments, the Pd/WO3 catalyst achieves an exceptional HCOOH yield of 4.67 mmol gcat-1 h-1 with a high selectivity of 62% under full-spectrum light irradiation at room temperature using molecular O2. Notably, these results significantly outperform the state-of-the-art photocatalytic systems operated under identical condition.

Heterogeneous Photocatalytic Strategies for C(sp3 )-H Activation

Activation of ubiquitous C(sp3 )-H bonds is extremely attractive but remains a great challenge. Heterogeneous photocatalysis offers a promising and sustainable approach for C(sp3 )-H activation and has been fast developing in the past decade. This Minireview focuses on mechanism and strategies for heterogeneous photocatalytic C(sp3 )-H activation. After introducing mechanistic insights, heterogeneous photocatalytic strategies for C(sp3 )-H activation including precise design of active sites, regulation of reactive radical species, improving charge separation and reactor innovations are discussed. In addition, recent advances in C(sp3 )-H activation of hydrocarbons, alcohols, ethers, amines and amides by heterogeneous photocatalysis are summarized. Lastly, challenges and opportunities are outlined to encourage more efforts for the development of this exciting and promising field.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Water Microdroplets-Initiated Methane Oxidation

The special redox reactivity of water microdroplets causes "mild ignition" of methane gas to form methane oxygenates. The C(sp3)-H bond of methane can be activated by the hydroxyl radical (OH·) or the hydrogen radical (H·) across the air-water interface (AWI) of microdroplets to generate the methyl radical (CH3·). Once CH3· is formed, it undergoes free-radical reactions with O2 in the air, excessive OH· and H· across the AWI, and H2O2 present at the AWI and generated CH3· itself to produce methanol and other species. Production of the methanol and other oxygenates was confirmed by gas chromatography, mass spectrometry, and 1H- and 13C-nuclear magnetic resonance. Formic acid, acetic acid, ethanol, carbon dioxide, and methyl peroxide were also detected as methane oxidation byproducts. This water microdroplet-initiated oxidation process can be further enhanced under ultrasonication to yield 2.66 ± 0.77 mM methanol conversion from the methane gas in a single spray run for 30 min, with a selectivity of 19.2% compared with all other oxygenated species.

Amorphous TiOx Stabilized Intermetallic Pt3Ti Nanocatalyst for Methanol Oxidation Reaction

Intermetallic compounds, featuring atomically ordered structures, have emerged as a class of promising electrocatalysts for fuel cells. However, it remains a formidable challenge to controllably synthesize Pt-based intermetallics during the essential high-temperature annealing process as well as stabilize the nanoparticles (NPs) during the electrocatalytic process. Herein, we demonstrated a Ketjen black supported intermetallic Pt₃Ti nanocatalyst coupled with amorphous TiO_x species (Pt₃Ti-TiO_x/KB). The TiO_x can not only confine Pt₃Ti NPs during the synthesis and electrocatalytic process by a strong metal-oxide interaction but also promote the water dissociation for generating more OH species, thus facilitating the conversion of CO_ad. The Pt₃Ti-TiO_x/KB showed a significantly enhanced mass activity (2.15 A mg_Pt^-1) for the methanol oxidation reaction, compared with Pt₃Ti/KB and Pt/C, and presented an impressively high mass activity retention (∼71%) after the durability test. This work provides an effective strategy of coupling Pt-based intermetallics with functional oxides for developing highly performed electrocatalysts.