Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co₂C for Syngas Conversion

Abstract

The design of supported heterogeneous catalysts requires a detailed understanding of the structure and chemistry of the active surface. Although the chemical components of the active phase, support material, and process feed are typically considered to be the most important factors governing catalyst structure and performance, many common commercial supports contain trace impurities, which can have profound effects on catalyst properties. In this work, we study silica‐supported cobalt‐based catalysts, which are widely used in syngas conversion to value‐added products. Supported metallic Co is a commercial Fischer‐Tropsch catalyst, whereas Co2C has shown promise for the direct conversion of syngas to higher oxygenates. This study examines the effects of Na, a commonly detected support impurity and a frequently used promoter, on the structure and reactivity of Co and Co2C. We show that trace Na impurities significantly decrease catalyst activity of supported metallic Co, and that high Na concentrations result in Co2C formation and a loss in Fischer‐Tropsch activity. However, in Co2C catalysts, Na plays an important role in stabilizing the Co2C phase, but excess Na decreases catalyst activity. We use in situ X‐ray absorption spectroscopy to study Co2C formation and decomposition in the Na‐free catalyst under carburization and reaction conditions. The work reveals the importance of carefully controlling alkali metal content, particularly at trace levels, in catalyst design.

Controlled Doping of Electrocatalysts through Engineering Impurities

“…Doping can be exploited to tailor the kinetics, selectivity, and stability of catalyst toward specific reactions. [39,40] As a platinum-group metal, Pd has similar electronic properties to Pt, but its stronger H absorption and adsorption behavior result in slow reaction rates in acidic-HOR. [10] Lattice distortions from the presence of B in bulk Pd [41] change its physical properties and B-doping modifies its catalytic activity.…”

Theoretical Insights into Morphologies of Alkali-Promoted Cobalt Carbide Catalysts for Fischer–Tropsch Synthesis

“…Previous studies suggested that the added alkali metals may act as electron donors to cobalt, leading to stronger adsorption and enhanced dissociation of CO, which also benefits the formation of the Co 2 C phase. 47,50 The olefin/paraffin (O/P) ratio and the CO 2 selectivity also increased upon alkali addition. 6 Furthermore, the FTS reaction has been shown to be a structure-sensitive reaction, as different facets of Co 2 C were found to exhibit distinct catalytic activities toward CO dissociation, hydrogenation, and chain growth.…”

Enhanced Growth in Atomic Layer Deposition of Ruthenium Metal: The Role of Surface Diffusion and Nucleation Sites

“…Atomic layer deposition (ALD) is an advanced thin film deposition technique that has gained wide interest for various technological applications in microelectronics, , catalysis, − and renewable energy. − ALD can be used to deposit a broad range of thin-film materials, including oxides, sulfides, and nitrides, as well as metals such as Ni, Cu, and noble metals. , ALD is a valuable vapor deposition technique due to its unique growth process wherein the precursors undergo alternating and self-limiting surface reactions. The layer-by-layer growth mechanism ideally leads to conformality and excellent control over the thickness.…”