Identifying the catalyst chemical state and adsorbed species during methanol conversion on copper using ambient pressure X-ray spectroscopies

Abstract

A model Cu catalyst surface oxidises to Cu2O when methanol, oxygen and water vapour are all present during methanol conversion.

Operando Surface Studies on Metal-Oxide Interfaces of Bimetal and Mixed Catalysts

“…It will cast light on the debated topic by gaining a fundamental insight into molecular behavior at the interface. However, several major challenges about operando techniques are constantly raised because of the poor reliability of data acquisitions by contamination or beam damage effect during experiments. , Therefore, there is plenty of room for exploration in operando surface chemistry for a robust foundation of future heterogeneous catalysis.…”

Methanol Decomposition on Copper Surfaces under Ambient Conditions: Mechanism, Surface Kinetics, and Structure Sensitivity

“…Methoxy is an important reaction intermediate that adsorbs strongly on Cu surfaces, making it easy to detect. Another surface species that was observed in AP-XPS studies is formate (HCOO*). − It is rather peculiar for formate to form in the absence of oxygen or water; we argued in our previous studies that this species might be related to external effects such as a compromised base pressure before the measurements or cross-contamination from previous experiments. ,, Such problems are common in shared user facilities, where most AP-XPS setups are located, due to constraints of the experimental schedule …”

“…Although both UHV studies and DFT calculations provide valuable information on the methanol–Cu interaction, they are not sufficient. Capturing important conceptual issues that come along with heterogeneous catalysis requires surface-sensitive spectroscopy experiments performed under ambient conditions. − Within this context, several studies were performed to investigate the interaction of methanol vapor in the mbar pressure range with various Cu surfaces in the past few years using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), sum frequency generation (SFG), and high-pressure scanning tunneling microscopy (HP-STM) techniques. − Unlike UHV studies, dry dehydrogenation of methanol into methoxy was observed even on high-coordinated surfaces. − Two effects contribute to this difference; the equilibrium shifts at ambient conditions compared to UHV conditions, and nonzero chemical potentials help to overcome the kinetic barriers . Methoxy is an important reaction intermediate that adsorbs strongly on Cu surfaces, making it easy to detect.…”

“…34−36 It is rather peculiar for formate to form in the absence of oxygen or water; we argued in our previous studies that this species might be related to external effects such as a compromised base pressure before the measurements or cross-contamination from previous experiments. 34,35,38 Such problems are common in shared user facilities, where most AP-XPS setups are located, due to constraints of the experimental schedule. 38 Despite AP-XPS being the most versatile and widely used technique in probing surfaces at ambient conditions, 39 there are two main challenges.…”

Revealing the Role of CO during CO2 Hydrogenation on Cu Surfaces with In Situ Soft X-Ray Spectroscopy

“…This could arise from oxygenated hydro- carbon contaminants, 31 with the corresponding component in the O 1s region convoluted into the larger OH−H 2 O peak, although this could also be assigned to formate. 29 Notably, the O* peak in the O 1s spectrum (Figure 2c(iv)) is greatly diminished in intensity relative to the other adsorbed and gas phase peaks when compared to Figure 2c(iii). This decrease is consistent with CO scavenging O* from the catalyst surface to form gas phase CO 2 , i.e., shifting the equilibrium of dissociative CO 2 adsorption (CO 2 ⇌ O* + CO).…”