# Thermocatalytic Behavior of TiO2 as a Dehydrogenation Catalyst: A Case Study of Methane Activation and Nonoxidative Coupling

## TL;DR

This paper studies how TiO2 can act as a catalyst for converting methane into useful hydrocarbons, finding that it has limitations but potential for improvement.

## Contribution

The study provides detailed mechanistic insights into methane activation and coupling on TiO2 using DFT calculations.

## Key findings

- CH3/CH2 coupling is more favorable than CH3/CH3 coupling for ethane formation.
- CH2/CH2 coupling to form ethylene has a lower activation barrier of 1.01 eV.
- Rutile TiO2 is not effective for NOCM due to high C–H activation energy and unstable intermediates.

## Abstract

The abundance of cheap natural gas has changed the energy
supply
landscape and spurred efforts to find alternative sources of energy
to traditional fossil fuels. Methane (CH4) is the primary
constituent of natural gas, and its C–H bond activation remains
a long-standing puzzle in the chemical industry. Transition-metal
oxides exhibit intrinsic Lewis acid–base properties beneficial
for activating the C–H bonds of CH4. In this work,
we investigated the nonoxidative coupling of CH4 (NOCM)
to C2 hydrocarbons on the rutile TiO2 (110)
surface at 1240 K by using density functional theory (DFT) calculations.
We explored three different CC coupling pathways for the formation
of ethane after the sequential activation of two CH4 molecules.
We found that CH3/CH3 coupling involves high
activation barriers, while the formation of C2H5 from the coupling of CH3/CH2 is kinetically
and thermodynamically more facile. Considering ethylene formation
routes, we found that the dehydrogenation of methyl species requires
high energy barriers. However, the subsequent CC coupling of CH2/CH2 occurs at a lower activation barrier of 1.01
eV. Moreover, our calculations revealed that the dehydrogenation of
C2H5 to form ethylene is favored over its hydrogenation
to form ethane. This work provides various mechanistic pathways that
can help in designing dehydrogenation catalysts with enhanced catalytic
activity. However, our results indicate that despite low barrier coupling
routes, rutile TiO2 alone is not an effective catalyst
for NOCM due to the energy-intensive C–H activation and limited
stability of reactive intermediates. Rutile TiO2 may have
enhanced activity and selectivity in doped configurations or as a
catalyst support within multifunctional catalytic systems.