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Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co 2 C for Syngas Conversion
Author(s) -
Asundi Arun S.,
Hoffman Adam S.,
Nathan Sindhu S.,
Boubnov Alexey,
Bare Simon R.,
Bent Stacey F.
Publication year - 2021
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202001703
Subject(s) - catalysis , syngas , fischer–tropsch process , cobalt , chemistry , oxygenate , impurity , chemical engineering , inorganic chemistry , metal , reactivity (psychology) , carbon monoxide , phase (matter) , materials science , selectivity , organic chemistry , engineering , medicine , alternative medicine , pathology
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 Co 2 C 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 Co 2 C. We show that trace Na impurities significantly decrease catalyst activity of supported metallic Co, and that high Na concentrations result in Co 2 C formation and a loss in Fischer‐Tropsch activity. However, in Co 2 C catalysts, Na plays an important role in stabilizing the Co 2 C phase, but excess Na decreases catalyst activity. We use in situ X‐ray absorption spectroscopy to study Co 2 C 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.