A DRIFTS study of CO adsorption and hydrogenation on Cu-based core–shell nanoparticles

Abstract

Core-shell nanoparticles are being considered for various applications due to their controllable atomic structure and improved properties compared to their bulk counterparts. In the present work, we have synthesized Cu@Mn 3 O 4 and Cu@Co 3 O 4 (core@shell) nanocatalysts using wet-chemical synthesis methods involving organic surfactants, and probed their surfaces using CO and H 2 under reaction conditions using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The surfactant ligands used in the synthesis of the nanoparticles must be removed to allow access to the active catalyst sites. These ligands can be removed by oxidation, allowing adsorption of CO and H 2 . This work reports the DRIFTS results of CO adsorption and hydrogenation on Cu@Mn 3 O 4 and Cu@Co 3 O 4 nanoparticles after removing the ligands. The CO hydrogenation results were in agreement with the DRIFTS results, which suggested that the Cu@Co 3 O 4 nanoparticles adsorb CO both dissociatively and associatively, creating a balance between molecular CO required for CO insertion and dissociated surface carbon species required for chain growth. This resulted in higher selectivities towards C 2+ alcohols on this catalyst. On the other hand, the Cu@Mn 3 O 4 nanoparticles showed a higher CO uptake and a lower CO dissociation activity, which resulted in a lower CH x concentration on the surface, thus limiting the rate of the CO insertion step required to form higher alcohols.

Spectrum baseline artefacts and correction of gas-phase species signal during diffuse reflectance FT-IR analyses of catalysts at variable temperatures

“…A DRIFTS reactor is particularly suited to this 7 type of investigation since the catalyst powder can be used directly as such and therefore 8 DRIFTS is becoming a major technique for catalytic applications at the gas-solid interface. 9 Some commercial DRIFTS cells enable using high reaction temperatures and high pressures 10 [19,20], whereas it is more difficult to built IR cell in transmission mode respecting these 11 experimental conditions [21]. 12 DRIFTS exhibits a higher sensitivity with respect to surface species and strongly 13 absorbing samples such as carbon-based materials can be studied [22].…”

“…16 In particular, DRIFTS analyses were able to show that the heat of CO adsorption on a Pt-Sn 17 alloy was about half the value measured on plain Pt, and that Pt-Sn segregation took place 18 reversibly in the presence of CO when the temperature was lower than 175°C [27]. DRIFTS 19 could also be used to investigate mass transport properties of zeolites, using sample masses 20 lower than 1 mg [28]. 21 This increased popularity is also due to the availability of a number of affordable 22 commercial cells, though those may exhibit hydrodynamic flaws [29,30] or important 23 temperature gradients that may need to be taken into account [31].…”

“…After drying at 120 °C for 12 h, the powder obtained was pretreated by a 3 citric acid solution with the molar ratio of Co 2+/ citric acid = 1/1.5 and then dried again at 120 4°C for 12 h. The sample was finally annealed in N 2 at 450 °C for 3 h. 17 18 High purity Ar, CO and H 2 were purchased from l'Air Liquide. The gases were used 19 without further purification. DRIFTS experiments were performed at ambient pressure with a 20 high temperature DRIFT cell (from Spectra-Tech) fitted with KBr windows, using a DRIFT- 21 II assembly.…”

“…15 The former path was estimated through the comparison of the absorbance signal of a 16 given CO feed measured in the DRIFTS fitted with a thin aluminium mirror placed on top of 17 the bed to that of the same feed measured in a gas-cell used in the transmission mode of 18 known pathlength. Note that both device temperatures were set to 80°C, to avoid differences 19 due to gas expansion. The area of the R-branch (band located at 2176 cm -1 in Fig.…”

In Situ-DRIFTS Study of Rh Promoted CuCo/Al2O3for Ethanol Synthesis via CO Hydrogenation

“…Fortunately, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is a powerful surface-sensitive technique to peer into the adsorption behavior of catalysts under reaction conditions. 19 Moreover, it is helpful to clarify the relation between the adsorption and reaction via probe molecule such as CO. 20 However, it was barely reported that DRIFTS was employed to characterize the Cu-Co based catalysts modified by rhodium to date. In this work, the CuCo/γ-Al 2 O 3 catalysts modified by rhodium were prepared and their CO hydrogenation activities were evaluated.…”