Alkali-induced effects on metal substrates and coadsorbed molecules

The role of potassium promoter in surface carbon hydrogenation on Hägg carbide surfaces

“…Intensive theoretical investigations into the mechanism of promotion (or poisoning) of chemisorption and reaction of CO, H 2 and N 2 by alkali ad-atoms have been reported [12,19,[25][26][27]. However, less mechanistic information of potassium promoter on CH 4 formation on transition metal surfaces is known.…”

Morphology control of K2O promoter on Hägg carbide (χ-Fe5C2) under Fischer–Tropsch synthesis condition

“…The generally accepted mechanism of alkali promotion is substrate-mediated electron transfer [6], enhanced surface electronic polarizability [13,14] as well as direct bonding between alkali and adsorbates [7,15]. Stolbov and Rahman [13,14] proposed that alkali adsorbates can dramatically enhance the electronic polarizability of the metal surface, while Liu et al [7] suggested that the promotion effect of alkali metal is short-ranged by forming direct K O bonding. However, all these effects cannot explain the drastic changes in catalytic performance caused by very low loadings of alkali promoters [16,17].…”

The Mechanism of Potassium Promoter: Enhancing the Stability of Active Surfaces

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Owing to their outstanding effect on improving catalytic reactivity, alkali-metal promoters have been widely used in industry [1,2] and extensively studied in academia. [3][4][5][6][7][8][9][10][11][12] Potassium-promoted iron catalysts for Fischer-Tropsch synthesis (FTS) and ammonia synthesis are the most representative examples of this effect. Owing to the complexity of real catalytic systems, the microscopic understanding of the alkalimetal promotion effect is still an elusive and challenging subject.In the past decades, most experimental and theoretical studies have focused on the co-adsorption systems involving alkali-metal atoms, for example, K + CO/metal.

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