Abstract
In this work, a statistical design and analysis platform was used to develop cobalt oxide based oxidation catalysts prepared via one pot metal salt reduction. An emphasis was placed upon understanding the effects of synthesis conditions, such as heating regimen and Co2+ concentration on the metal salt reduction mechanism, the resultant nanomaterial properties (i.e., size, crystal structure, and crystal faceting), and the catalytic activity in CO oxidation. This was accomplished by carrying out XRD, TEM, and FTIR studies on synthesis intermediates and products. Additionally, high-throughput experimentation was employed to study the performance of Co3O4 oxidation catalysts over a wide range of reaction conditions using a 16-channel fixed bed reactor equipped with a parallel infrared imaging system. Specifically, Co3O4 nanomaterials of varying properties were evaluated for their performance as CO oxidation catalysts. Figure-of-merits including light-off temperatures and activation energies were measured and mapped back to the catalyst properties and synthesis conditions. Statistical analysis methods were used to elucidate significant property-activity relationships as well as the design rules relevant in the synthesis of active catalysts. It was found that the degree of grain boundary consolidation and anisotropic growth in fcc and hcp CoO intermediates significantly influenced the catalytic activity. By utilizing the discovered synthesis-structure-activity relationships, CO oxidation light off temperatures were decreased to <90°C.
Highlights
Colloidal synthesis of nanoparticles is a versatile approach used to prepare materials with drastically different properties, potentially allowing them to be tailored for a wide range of applications in medicine, catalysis, and more (Qi, 2010)
Iterative statistical design of experiments and high-throughput screening were used to study the effect of synthesis parameters in the one-pot colloidal synthesis of CoOx on nanoparticle properties and catalytic activity in CO oxidation
Of the six variables studied, it was found that the concentration of CoAc used in the synthesis together with the synthesis aging temperature had the most significant impact on nanoparticle structure and catalyst activity with light off temperatures below 90◦C occurring above 0.06M CoAc and below 250◦C
Summary
Colloidal synthesis of nanoparticles is a versatile approach used to prepare materials with drastically different properties, potentially allowing them to be tailored for a wide range of applications in medicine, catalysis, and more (Qi, 2010). Control over the Co3O4 cation distribution has been the subject of a great deal of research, as Co3+ surface enrichment and control over the Co3+/ Co2+ ratio have been established to dramatically affect specific reaction rates, stabilities, and lightoff temperatures for many catalytic applications (Xie et al, 2009; Alvarez et al, 2012; Yu et al, 2013; Stelmachowski et al, 2014; Wen et al, 2014) This structure sensitivity is, in one form or another, a consequence of the preparation conditions and variables used in the preparation of the cobalt oxide catalyst.
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