Chapter 3
Heterogeneous and Homogeneous
Catalytic Partial Oxidations of Methane
to Methanol and Its Derivatives
3.1 Introduction
As described in Chapter 2, the conversion of methane to methanol via direct
oxidation of methane with molecular oxygen at ambient temperature and pressure
has been established in biological systems. On the other hand, the development
of an artificial, energy-efficient, one-step process for the production of methanol
from methane using molecular oxygen as the oxidant is still one of the most challenging transformations. Such a process would be attractive, as it could potentially
compete with the conventional production of methanol from methane via steam
reforming and subsequent methanol synthesis. Therefore, great efforts have been
expended to develop heterogeneous and homogeneous catalysts for the molecular
oxygen-mediated oxidation of methane to methanol. This chapter presents important
examples of the synthetic homogeneous and heterogeneous catalytic systems for
the oxidation of methane to methanol, with emphasis on one-step catalytic systems
that do not require strong oxidants. However, some systems that do not meet these
conditions but have provided motivation or direction in this field are also described.
While multi-stage processes for the conversion of methane to methanol are more
feasible than one-step catalytic processes, they are also more complex and less
efficient, and therefore less economical. In the multi-stage processes, methanol is
adsorbed on a solid surface or is derivatized once produced. In the heterogeneous
systems, methoxy species are adsorbed on the solid surface. Therefore, an additional
stage is required for the extraction of methanol with water. At the same time, the production from methane via methanol derivatives by using homogeneous catalysts also
requires the additional stage for the conversion of methanol derivatives to methanol
via processes such as hydrolysis. The methanol adsorbed on the solid surface or
derivatized methanol can be considered protected or stabilized methanol, which is
not oxidized further by the catalysts. Therefore, the conversion of methane to the
methanol adsorbed on the solid surface or the derivatized methanol may be useful methods for obtaining methanol in high yield. Therefore, this chapter presents
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_3
53
Heterogeneous and Homogeneous
Catalytic Partial Oxidations of Methane
to Methanol and Its Derivatives
3.1 Introduction
As described in Chapter 2, the conversion of methane to methanol via direct
oxidation of methane with molecular oxygen at ambient temperature and pressure
has been established in biological systems. On the other hand, the development
of an artificial, energy-efficient, one-step process for the production of methanol
from methane using molecular oxygen as the oxidant is still one of the most challenging transformations. Such a process would be attractive, as it could potentially
compete with the conventional production of methanol from methane via steam
reforming and subsequent methanol synthesis. Therefore, great efforts have been
expended to develop heterogeneous and homogeneous catalysts for the molecular
oxygen-mediated oxidation of methane to methanol. This chapter presents important
examples of the synthetic homogeneous and heterogeneous catalytic systems for
the oxidation of methane to methanol, with emphasis on one-step catalytic systems
that do not require strong oxidants. However, some systems that do not meet these
conditions but have provided motivation or direction in this field are also described.
While multi-stage processes for the conversion of methane to methanol are more
feasible than one-step catalytic processes, they are also more complex and less
efficient, and therefore less economical. In the multi-stage processes, methanol is
adsorbed on a solid surface or is derivatized once produced. In the heterogeneous
systems, methoxy species are adsorbed on the solid surface. Therefore, an additional
stage is required for the extraction of methanol with water. At the same time, the production from methane via methanol derivatives by using homogeneous catalysts also
requires the additional stage for the conversion of methanol derivatives to methanol
via processes such as hydrolysis. The methanol adsorbed on the solid surface or
derivatized methanol can be considered protected or stabilized methanol, which is
not oxidized further by the catalysts. Therefore, the conversion of methane to the
methanol adsorbed on the solid surface or the derivatized methanol may be useful methods for obtaining methanol in high yield. Therefore, this chapter presents
© Springer Nature Singapore Pte Ltd. 2020
T. Baba and A. Miyaji, Catalysis and the Mechanism of Methane Conversion to Chemicals,
https://doi.org/10.1007/978-981-15-4132-2_3
53