Impact of Nanoparticle–Support Interactions in Co₃O₄/Al₂O₃ Catalysts for the Preferential Oxidation of Carbon Monoxide

Abstract

Different supporting procedures were followed to alter the nanoparticle–support interactions (NPSI) in two Co3O4/Al2O3 catalysts, prepared using the reverse micelle technique. The catalysts were tested in the dry preferential oxidation of carbon monoxide (CO-PrOx) while their phase stability was monitored using four complementary in situ techniques, viz., magnet-based characterization, PXRD, and combined XAS/DRIFTS, as well as quasi in situ XPS, respectively. The catalyst with weak NPSI achieved higher CO2 yields and selectivities at temperatures below 225 °C compared to the sample with strong NPSI. However, relatively high degrees of reduction of Co3O4 to metallic Co were reached between 250 and 350 °C for the same catalyst. The presence of metallic Co led to the undesired formation of CH4, reaching a yield of over 90% above 300 °C. The catalyst with strong NPSI formed very low amounts of metallic Co (less than 1%) and CH4 (yield of up to 20%) even at 350 °C. When the temperature was decreased from 350 to 50 °C under the reaction gas, both catalysts were slightly reoxidized and gradually regained their CO oxidation activity, while the formation of CH4 diminished. The present study shows a strong relationship between catalyst performance (i.e., activity and selectivity) and phase stability, both of which are affected by the strength of the NPSI. When using a metal oxide as the active CO-PrOx catalyst, it is important for it to have significant reduction resistance to avoid the formation of undesired products, e.g., CH4. However, the metal oxide should also be reducible (especially on the surface) to allow for a complete conversion of CO to CO2 via the Mars–van Krevelen mechanism.

Ligand‐Protected Ultrasmall Pd Nanoclusters Supported on Metal Oxide Surfaces for CO Oxidation: Does the Ligand Activate or Passivate the Pd Nanocatalyst?

“…Figure 6‐II displays the temperature dependence of the CO oxidation over the 1 wt% Pd n (L‐Cys) m /CeO 2 , Pd n (L‐Cys) m /TiO 2 , Pd n (L‐Cys) m /Fe 3 O 4 , and Pd n (L‐Cys) m /ZnO catalysts. The highest catalytic activity is observed on the CeO 2 , TiO 2 and Fe 3 O 4 oxides which confirms that the reducibility of the metal oxides by the CO gas contributes to the observed low temperature activity [41–43] . It is also clear that the catalytic activity of the ligand‐protected Pd n (L‐Cys) m cluster is nearly similar on the three reducible oxides where 50 % and 100 % CO conversions occur at 88–92 °C and 110–115 °C, respectively.…”

Template-free Synthesis of Stable Cobalt Manganese Spinel Hollow Nanostructured Catalysts for Highly Water-Resistant CO Oxidation

“…The Mars-van Krevelen (MvK) mechanism has been widely used to describe the CO oxidation reaction (Widmann and Behm, 2014, Nyathi et al., 2019). CO oxidation on prepared cobalt manganese spinels also follows the MvK mechanism, the details of which are as follows.…”

Practical guide for x-ray photoelectron spectroscopy: Applications to the study of catalysts

“…providing the user has a well characterized energy scale 34 , however catalytic materials are typically insulating. The choice of a well-defined and stable reference point is therefore a paramount concern to the analyst as significant shifts in the binding energy of the supported nanoparticles can occur depending on, for example, support composition, alloy formation, the interaction with the support and SMSI effects, or nanoparticle size and shape 10,[35][36][37][38][39][40] .…”

“…To aid development of such catalytic systems, modification of the surface chemical, electronic and structural properties is of extreme importance and with their inherent surface sensitivity and chemical specificity, 4,5 X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) have become powerful tools in the armory of the catalytic scientist. 4,[6][7][8][9][10][11][12] Catalytic materials present some distinct challenges when it comes to surface analysis: they are often high surface area powders; usually insulating and the loading of the nanoparticulate active component can be very low (0.5 wt% or lower). XPS requires ultra-high vacuum (UHV) whilst most heterogeneous catalytic reactions take place at high pressures and temperatures, so catalytic materials are typically studied under conditions significantly different to that in which they would normally operate.…”