Disentangling Electronic and Geometric Effects in Electrocatalysis through Substitution in Isostructural Intermetallic Compounds

Abstract

Efficient development of catalytic materials requires knowledge of the decisive parameters defining the catalytic properties. In multicomponent metallic catalysts, these are categorized as electronic and geometric effects, yet they are strongly interrelated. A systematic disentanglement can be achieved by fixing one parameter while altering the other, which becomes possible through the substitution in isostructural intermetallic compounds. This approach enables the evaluation of electronic or geometric contributions both individually and combined. Herein, this is achieved by substitution of indium (three valence electrons) with tin (four valence electrons) in the series In1–x Sn x Pd2, which allows for a systematic variation of the total number of electrons per unit cell with only a minor variation of the unit cell parameters and thus the evaluation of the electronic effect. Geometric effects were evaluated by substitution of indium with gallium in the Ga1–x In x Pd2 series, which allows for a systematic variation of the interatomic distances while maintaining the same number of valence electrons per unit cell and close atomic coordinates. By substituting gallium with tin in the Ga1–x Sn x Pd2 series, both effects are combined and addressed simultaneously. The activity enhancement of the methanol oxidation reaction on the Ga1–x Sn x Pd2 series is attributed to the synergy of the combined effects.

Chemical Bonding in the Catalytic Platform Material Ga1‐xSnxPd2

“…The sum of all three results in the linear increase of the unit cell volume depending on x . [ 24 , 41 ]…”

“…Thereby, the values of a and c show slightly positive, the values of b slightly negative deviation from linearity. The sum of all three results in the linear increase of the unit cell volume depending on x [24,41] …”

“…Moreover, due to the higher Pd content, such centers may be formed by more than one Pd atom, that is, creating distinct conditions for the adsorption of acetylene molecules, which correlates with the higher catalytic selectivity of Ga 1-x Sn x Pd 2 in comparison with other GaÀ Pd compounds. [3,24] From the above analysis one may also recognize that the charge transfer and the d states of Pd crucially influence the catalytic activity of Ga 1-x Sn x Pd 2 materials. In the position space representation, this finds an additional rather unusual visualization in the relation between the QTAIM atomic shapes and ELIÀ D core shapes (Figure 7).…”

“…These include the selective hydrogenation of acetylene, which is an important industrial process to clean the ethylene feed for the production of polyethylene (80×10 6 t/a [3] ) or ethylene oxide (10×10 6 t/a [4] ) in the gas phase[ 5 , 6 , 7 , 8 ] (also propyne [9] ) and in the liquid phase, [10] furthermore in methanol steam reforming to release high‐purity hydrogen from methanol/water mixtures,[ 12 , 13 , 14 , 15 ] and finally in the synthesis of methanol from CO [16] or CO 2 ,[ 16 , 17 , 18 , 19 , 20 , 21 , 22 ] as well as for the synthesis of dimethyl ether (DME) from CO and the electrocatalytic hydrogen evolution reaction [23] or methanol oxidation reaction. [24] The latter reactions, in particular, enable an efficient synthesis, or use of, methanol/DME as chemical storage molecules for a hydrogen‐based energy infrastructure ( methanol economy [25] ).…”

Trendbericht Festkörperchemie 2023

“…61) Anhand der isotypen Reihen in den intermetallischen Verbindungen In 1-x Sn x Pd 2 und Ga 1-x Sn x Pd 2 haben Armbrüster, Grin und Mitarbeitende untersucht, wie elektronische und geometrische Einflüsse die elektrochemische Methanoloxidation beeinflussen. 62) Die Substitution von In durch Sn diente hierbei der Variation der elektronischen Konfiguration, während die Substitution von In durch Ga die geometrischen Einflüsse aufdeckte. Anschließende Untersuchungen am System Ga 1-x Sn x Pd 2 variierte diese beeinflussenden Parameter simultan für eine systematisch verbesserte Katalyseaktivität.…”