Oxidative Activation of Metal-Exchanged
Zeolite Catalysts for Methane
Hydroxylation
Muhammad Haris Mahyuddin
Abstract The stepwise approach of methane direct conversion to methanol by Feand Cu-exchanged zeolite catalysts involves a pre-activation of the catalysts by an
oxidant at high temperature. Since an isothermal process of this approach at temperature below 200 °C is highly desirable, understanding the mechanism of the oxidative
activation is important for developing strategies to reduce the activation temperature. In this chapter, I provide an overview of recent theoretical understanding in the
mechanisms of the Fe- and Cu-oxo active site formations from N 2 O, H 2 O 2 , and O 2
activations. Density functional theory calculations show that N 2 –O, HO–OH, and
O=O cleavages on the reduced Fe and Cu centers can actually be achieved with
low activation barriers. However, as also suggested by recent experimental works,
high temperature is required to form the precursors, i.e. the reduced metal centers. I
conclude this overview with forward looking aspects that should be addressed in the
future.
Keywords Catalyst activation by oxidant · Active site formation · Iron · Copper ·
Zeolites
1 Introduction
As also described in Chap. 4, methane hydroxylation by metal-exchanged zeolites
is in general a stepwise (stoichiometric looping) process although the continuous
(catalytic) process is also available but disfavored due to its low methanol yield and
selectivity [1, 2]. As shown in Fig. 1, the stepwise process involves three separate
steps including (1) activation of the metal–zeolite catalyst by an oxidant at high
temperature, (2) methane reaction at temperatures below 200 °C, and (3) methanol
extraction using a solvent or steam at 25–200 °C. A number of successful experiments have been reported for Fe- and Cu-exchanged zeolites. Panov and co-workers
M. H. Mahyuddin (B)
Research Group of Advanced Functional Materials, Faculty of Industrial Technology,
Institut Teknologi Bandung, Bandung 40132, Indonesia
e-mail: haris@tf.itb.ac.id
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_5
87
Zeolite Catalysts for Methane
Hydroxylation
Muhammad Haris Mahyuddin
Abstract The stepwise approach of methane direct conversion to methanol by Feand Cu-exchanged zeolite catalysts involves a pre-activation of the catalysts by an
oxidant at high temperature. Since an isothermal process of this approach at temperature below 200 °C is highly desirable, understanding the mechanism of the oxidative
activation is important for developing strategies to reduce the activation temperature. In this chapter, I provide an overview of recent theoretical understanding in the
mechanisms of the Fe- and Cu-oxo active site formations from N 2 O, H 2 O 2 , and O 2
activations. Density functional theory calculations show that N 2 –O, HO–OH, and
O=O cleavages on the reduced Fe and Cu centers can actually be achieved with
low activation barriers. However, as also suggested by recent experimental works,
high temperature is required to form the precursors, i.e. the reduced metal centers. I
conclude this overview with forward looking aspects that should be addressed in the
future.
Keywords Catalyst activation by oxidant · Active site formation · Iron · Copper ·
Zeolites
1 Introduction
As also described in Chap. 4, methane hydroxylation by metal-exchanged zeolites
is in general a stepwise (stoichiometric looping) process although the continuous
(catalytic) process is also available but disfavored due to its low methanol yield and
selectivity [1, 2]. As shown in Fig. 1, the stepwise process involves three separate
steps including (1) activation of the metal–zeolite catalyst by an oxidant at high
temperature, (2) methane reaction at temperatures below 200 °C, and (3) methanol
extraction using a solvent or steam at 25–200 °C. A number of successful experiments have been reported for Fe- and Cu-exchanged zeolites. Panov and co-workers
M. H. Mahyuddin (B)
Research Group of Advanced Functional Materials, Faculty of Industrial Technology,
Institut Teknologi Bandung, Bandung 40132, Indonesia
e-mail: haris@tf.itb.ac.id
© Springer Nature Singapore Pte Ltd. 2020
K. Yoshizawa (ed.), Direct Hydroxylation of Methane,
https://doi.org/10.1007/978-981-15-6986-9_5
87