Scientists at the US Department of Energy’s (DOE) Brookhaven National Laboratory and collaborating institutions have engineered a highly selective catalyst that can convert methane, a major component of natural gas, into methanol, an easily transportable liquid fuel, in a single, one-step reaction. As described in a paper just published in the Journal of the American Chemical Society, this direct process for methane-to-methanol conversion runs at a temperature lower than required to make tea and exclusively produces methanol without additional byproducts.

That marks a big advance over more complex traditional conversions that typically require three separate reactions, each under different conditions, including vastly higher temperatures.

The simplicity of the system could make it particularly useful for tapping “stranded” natural gas reserves in isolated rural areas, far from the costly infrastructure of pipelines and chemical refineries, said Brookhaven chemist and study co-author Sanjaya Senanayake. Such local deployments would remove the need to transport high-pressure, flammable liquified natural gas.

Brookhaven Science Associates, which manages Brookhaven Lab on behalf of DOE, and the University of Udine, collaborators in this work, have filed a patent cooperation treaty application on the use of the catalyst for one-step methane conversion. The team is exploring ways to work with entrepreneurial partners to bring the technology to market.

The basic science behind the conversion builds on a decade of collaborative research. The Brookhaven chemists worked with experts at the Lab’s National Synchrotron Light Source II (NSLS-II) and Center for Functional Nanomaterials (CFN)—two DOE Office of Science user facilities that have a wide range of capabilities for tracking the intricacies of chemical reactions and the catalysts that enable them —as well as researchers at DOE’s Ames National Laboratory and international collaborators in Italy and Spain.

Earlier studies worked with simpler ideal versions of the catalyst, consisting of metals on top of oxide supports or inverted oxide on metal materials. The scientists used computational modeling and a range of techniques at NSLS-II and CFN to learn how these catalysts work to break and remake chemical bonds to convert methane to methanol and to elucidate the role of water in the reaction.

High-resolution electron microscopy images of the catalyst captured at the CFN. Frame A shows the catalyst with a scale bar representing 20 nanometers (nm) after three consecutive reaction cycles; B zooms in to reveal surface details; C provides a composite elemental map, with individual elements shown in D, E, and F. Together the images reveal that the active metal, palladium (Pd), is highly dispersed on the supporting cerium (Ce) substrate with a thin layer of carbon (C) at the interface. (Sooyeon Hwang/Brookhaven National Laboratory)

The catalyst contains a thin layer of interfacial carbon between the metal and oxide.

Carbon is often overlooked as a catalyst. But in this study, we did a host of experiments and theoretical work that revealed that a fine layer of carbon between palladium and cerium oxide really drove the chemistry. It was pretty much the secret sauce. It helps the active metal, palladium, convert methane to methanol

—Juan Jimenez, a Goldhaber postdoctoral fellow in Brookhaven Lab’s Chemistry Division and the lead author on the paper

To explore and ultimately reveal this unique chemistry, the scientists built new research infrastructure both in the Catalysis Reactivity and Structure group’s laboratory in the Chemistry Division and at NSLS-II.

This is a three-phase reaction with gas, solid, and liquid ingredients—namely methane gas, hydrogen peroxide and water as liquids, and the solid powder catalyst—and these three ingredients react under pressure. So, we needed to build new pressurized three-phase reactors so we could monitor those ingredients in real time.

—Sanjaya Senanayake

In the end, the team discovered how the active state of their three-component catalyst—made of palladium, cerium oxide, and carbon—exploits the complex three-phase, liquid-solid-gas microenvironment to produce the final product.

Now, instead of needing three separate reactions in three different reactors operating under three different sets of conditions to produce methanol from methane with the potential of byproducts that require costly separation steps, the team has a three-part catalyst that drives a three-phase reaction all in one reactor with 100% selectivity for methanol production.

Resources

• From Methane to Methanol: Pd-iC-CeO₂ Catalysts Engineered for High Selectivity via Mechanochemical Synthesis; Juan D. Jiménez, Pablo G. Lustemberg, Maila Danielis, Estefanía Fernández-Villanueva, Sooyeon Hwang, Iradwikanari Waluyo, Adrian Hunt, Dominik Wierzbicki, Jie Zhang, Long Qi, Alessandro Trovarelli, José A. Rodriguez, Sara Colussi, M. Verónica Ganduglia-Pirovano, and Sanjaya D. Senanayake Journal of the American Chemical Society doi: 10.1021/jacs.4c04815