Electrocatalytic Shilov chemistry for the oxidation of aliphatic groups

Electrocatalytic water-to-oxygenates conversion: redox-mediated versus direct oxygen transfer

Electrocatalytic oxygenation of hydrocarbons with high selectivity has attracted much attention for its advantages in the sustainable and controllable production of oxygenated compounds with reduced greenhouse gas emissions. Especially when utilizing water as an oxygen source, by constructing a water-to-oxygenates conversion system at the anode, the environment and/or energy costs of producing oxygenated compounds and hydrogen energy can be significantly reduced. There is a broad consensus that the generation and transformation of oxygen species are among the decisive factors determining the overall efficiency of oxygenation reactions. Thus, it is necessary to elucidate the oxygen transfer process to suggest more efficient strategies for electrocatalytic oxygenation. Herein, we introduce oxygen transfer routes through redox-mediated pathways or direct oxygen transfer methods. Especially for the scarcely investigated direct oxygen transfer at the anode, we aim to detail the strategies of catalyst design targeting the efficient oxygen transfer process including activation of organic substrate, generation/adsorption of oxygen species, and transformation of oxygen species for oxygenated compounds. Based on these examples, the significance of balancing the generation and transformation of oxygen species, tuning the states of organic substrates and intermediates, and accelerating electron transfer for organic activation for direct oxygen transfer has been elucidated. Moreover, greener organic synthesis routes through heteroatom transfer and molecular fragment transfer are anticipated beyond oxygen transfer.

Methane Oxidation to Methanol

The direct transformation of methane to methanol remains a significant challenge for operation at a larger scale. Central to this challenge is the low reactivity of methane at conditions that can facilitate product recovery. This review discusses the issue through examination of several promising routes to methanol and an evaluation of performance targets that are required to develop the process at scale. We explore the methods currently used, the emergence of active heterogeneous catalysts and their design and reaction mechanisms and provide a critical perspective on future operation. Initial experiments are discussed where identification of gas phase radical chemistry limited further development by this approach. Subsequently, a new class of catalytic materials based on natural systems such as iron or copper containing zeolites were explored at milder conditions. The key issues of these technologies are low methane conversion and often significant overoxidation of products. Despite this, interest remains high in this reaction and the wider appeal of an effective route to key products from C-H activation, particularly with the need to transition to net carbon zero with new routes from renewable methane sources is exciting.

Catalytic Oxidation of Methane to Oxygenated Products: Recent Advancements and Prospects for Electrocatalytic and Photocatalytic Conversion at Low Temperatures

Methane is an important fossil fuel and widely available on the earth's crust. It is a greenhouse gas that has more severe warming effect than CO2. Unfortunately, the emission of methane into the atmosphere has long been ignored and considered as a trivial matter. Therefore, emphatic effort must be put into decreasing the concentration of methane in the atmosphere of the earth. At the same time, the conversion of less valuable methane into value-added chemicals is of significant importance in the chemical and pharmaceutical industries. Although, the transformation of methane to valuable chemicals and fuels is considered the "holy grail," the low intrinsic reactivity of its C-H bonds is still a major challenge. This review discusses the advancements in the electrocatalytic and photocatalytic oxidation of methane at low temperatures with products containing oxygen atom(s). Additionally, the future research direction is noted that may be adopted for methane oxidation via electrocatalysis and photocatalysis at low temperatures.

Electrochemical Reoxidation Enables Continuous Methane-to-Methanol Catalysis with Aqueous Pt Salts

The direct conversion of methane to methanol would enable better utilization of abundant natural gas resources. In the presence of stoichiometric Pt^IV oxidants, Pt^II ions are capable of catalyzing this reaction in aqueous solutions at modest temperatures. Practical implementation of this chemistry requires a viable strategy for replacing or regenerating the expensive Pt^IV oxidant. Herein, we establish an electrochemical strategy for continuous regeneration of the Pt^IV oxidant to furnish overall electrochemical methane oxidation. We show that Cl-adsorbed Pt electrodes catalyze facile oxidation of Pt^II to Pt^IV at low overpotential without concomitant methanol oxidation. Exploiting this facile electrochemistry, we maintain the Pt^II/IV ratio during Pt^II-catalyzed methane oxidation via in situ monitoring of the solution potential coupled with dynamic modulation of the electric current. This approach leads to sustained methane oxidation catalysis with 70% selectivity for methanol.