Chinese scholars have made progress in the activation of inert C-H bonds

Fig.
Room temperature visible light based on "single atom Pt assembly" catalytic material drives the reaction of cyclohexane with methane oxygen-free dehydrogenation

With the support of the National Natural Science Foundation of China (grant number: 92061105, 21875090), Professor Li Lu's team at Jilin University has made progress
in the preparation of "single atom ensemble" catalysts and the activation of light-driven inert C-H bonds 。 The results, titled "Visible-light-driven non-oxidative dehydrogenation of alkanes at ambient conditions," were published in Nature Energy on September 29
, 2022 。 Links to papers: _istranslated="1">.

The efficient use of abundant and stable saturated alkanes under mild environmental conditions has always been one of
the most challenging topics in the field of energy and catalysis.
Due to the intrinsic stability and poor electron affinity of sp³ hybrid C-H bonds, non-oxidative dehydrogenation of alkanes is thermodynamically unfavorable, and the activation of hydrocarbon bonds in broken alkanes usually requires high temperature, isostoichiometry oxidant or high-energy ultraviolet treatment, which not only consumes large energy consumption, but also leads to rapid deactivation
of the catalyst.
Using solar energy to trigger the dehydrogenation reaction of alkanes can break the limits of thermodynamic equilibrium and achieve the conversion
of alkanes under milder conditions.
Therefore, the development of a photocatalyst that can use visible and infrared light in sunlight to drive the non-oxygen dehydrogenation reaction of alkanes has important basic research value and application prospects
.

In view of the above problems, the research team used the "reduction-oxidation-reconstruction" strategy to prepare a new "single-atom Pt set" (referring to several Pt monomer PtClO₃ close to each other, but not directly bonded) modified black titanium dioxide photocatalyst
.
The catalyst can show good alkane dehydrogenation performance at room temperature, and the light response covers the visible to near-infrared light bands
.
In the catalytic cyclohexane dehydrogenation reaction, the maximum dehydrogenation conversion rate of the catalyst is close to 1500 mmol gPt-1 ^min-1, and it remains highly active after 80 cycles, with an average cumulative conversion of 100,000 hydrogen
per Pt atom.
In the methane dehydrogenation reaction, the single conversion of methane can be 8.
2% with the use of this catalyst, and the selectivity of propane in the product is 65%.

Unlike conventional methane dehydrogenation coupling reactions to produce ethane, the direct and highly selective conversion of methane to propane has been reported very
rarely.
The team further investigated the reaction mechanism, and the results showed that methane undergoes intramolecular dehydrogenation to form carbene intermediates, and the introduction of Pt aggregation catalysts allows methane to selectively produce propane
through methyl carbene intermediates.
In contrast, conventional single-atom catalysts do not provide the adjacent polymetallic sites required for the reaction
.

This series of studies revealed that the aggregation degree of Pt collection plays a decisive role in the reaction pathway and product selectivity, and at the same time, regulating the oxidation state of Pt monomers can also affect
the photocatalytic performance.
The research results have important guiding significance
for the design and development of high-efficiency photocatalysts.