CO as a Probe Molecule to Study Surface Adsorbates during Electrochemical Oxidation of Propene

Abstract

A major challenge in the electrochemical oxidation of hydrocarbons is understanding the formation of intermediate species, some of which continue to react, while others are non‐reactive or poisonous species that block adsorption of further reactants. Herein we investigate the identity and behavior of adsorbates formed during partial oxidation of propene. We employ two techniques: Electrochemistry‐Mass Spectrometry (EC‐MS) and Attenuated Total Reflection Infrared Spectroscopy (ATR‐FTIR). In both cases, we use CO as a probe molecule, to perturb the ad‐layer of propene intermediates. In the EC‐MS experiments, propene and its intermediates were quantified by triggering their desorption via displacement with CO. We show evidence for at least two distinct classes of propene adsorbates, via CO displacement and electrochemical stripping. A redshift in the ν(C−O) mode was observed, during IR spectroscopy, reflecting the chemical environment arising from strongly bound propene intermediates.

The low overpotential regime of acidic water oxidation part I: the importance of O2 detection

“…This enables the ultrasensitive detection of electrochemically produced O 2 and thus accurate measurement of OER activity in spite of the challenges highlighted above. This EC-MS setup allows for 100% collection efficiency and well-characterized reproducible mass transport, allowing quantitative real-time detection of gaseous electrochemical desorption products at sub-picomol per second sensitivity, 47,48 contributing to the unravelling of the mechanisms of electrocatalytic hydrogen evolution, 48 CO reduction, 49 propene oxidation, 50,51 and CO oxidation. 47,52,53 It has been used previously for isotope-labeling experiments in the OER, 53,54 but its sensitivity has not previously been utilized to push the limits of accurate activity measurements.…”

Rational Catalyst Design for Higher Propene Partial Electro-oxidation Activity by Alloying Pd with Au

“…We consider this elementary step as representative for propene degradation, being the most favored initiation for propene breakdown in carbonaceous fragments. At operating potentials, further oxidation and cleavage of *CH 2 + *CHCH 2 is thermodynamically favored; a thorough discussion of this pathway is reported in our previous work , and is out of scope herein. Propene degradation on pure Pd is a key mechanism that affects selectivity .…”

“…Increased availability and falling prices for electricity from renewable sources such as wind and solar make electrification of the chemical industry (often termed Power-to-X) ever more interesting. − One such process is the oxidation of propene to the commodity chemicals acrolein and acrylic acid, which are produced on the megaton scale annually . Direct electrochemical oxidation of propene has been investigated on various catalytic systems, both in acidic and in alkaline environments. − We have previously reported that on palladium, a layer of strongly bound partially oxidized propene-derived species (degradation species) forms in situ from propene, which steers the selectivity of the catalyst by stabilization of allyl adsorption over vinyl adsorption. , While high selectivity toward the allyl oxidation products (allyl alcohol, acrolein, and acrylic acid) is achieved, reaction rates are extremely low due to the high coverage of the surface with unreactive, propene-derived species.…”

“…7−14 We have previously reported that on palladium, a layer of strongly bound partially oxidized propene-derived species (degradation species) forms in situ from propene, which steers the selectivity of the catalyst by stabilization of allyl adsorption over vinyl adsorption. 15,16 While high selectivity toward the allyl oxidation products (allyl alcohol, acrolein, and acrylic acid) is achieved, reaction rates are extremely low due to the high coverage of the surface with unreactive, propene-derived species.…”

Reaction Mechanism and Selectivity Tuning of Propene Oxidation at the Electrochemical Interface

“…Propene is an important feedstock (over 130 million tons of capacity) for manufacturing numerous commodity chemicals in the industry. − Traditionally, propene conversion is via thermocatalysis. With the dramatic increase in available renewable electricity in recent years, directly converting propene via electrochemical approaches under moderate conditions becomes a capable alternative. − As an anodic reaction, propene oxidation may replace the oxygen evolution reaction in electrolyzers to couple with cathodic hydrogen evolution or the CO 2 reduction reaction. The lower working potential of propene oxidation than the OER and high value-added products rather than O 2 can greatly benefit the energy efficiency and economic effectiveness of the electrolyzers .…”