Balanced, strong interaction of Ni–Na₂O–ZrO₂catalyst components under CO₂reforming of methane is a criterion of good catalytic activity and stability.

Recently a new In-promoted Ni catalyst has been elaborated and published in our laboratory, that has beneficial properties in dry reforming of methane, including inhibited coking. In order to get deeper insights into the coke-free behavior of this SiO₂-supported 3wt% Ni 2wt% In catalyst, we wished to monitor the interaction between CO and the catalyst. For this purpose DRIFTS studies under CO, CO₂ or CO₂+CH₄ flow at different temperatures and CO pulse flow experiments at 600 ^oC followed by mass spectrometry were carried out. A linear carbonyl band at 2013 cm^-1 in the DRIFT spectra of the In-promoted catalyst was attributed to CO bonded on Ni atoms surrounded by In neighbors. The lack of bridge and multi-coordinated carbonyls also proved the dilution of Ni surface with In. In the presence of a CH₄:CO₂=70:30 dry reforming mixture, stable Ni bonded CO species were found on NiIn/SiO₂ suggesting that the metallic sites remained clean during the reaction (unlike on the reference Ni/SiO₂). At the end of the reforming reaction, little surface segregation of the original bimetallic particles and the formation of islands with adjacent Ni sites were presumed based on the DRIFTS results. The pulse CO experiments at 600 ^oC, tailored to detect the most sensitive surface sites for Boudouard reaction, proved that CO dissociation on the bimetallic catalyst was markedly hindered, while it caused carbon deposition on the unpromoted sample. Based on all these results, we postulate a picture of the working catalyst that is dispersed ensembles of NiIn-InO_x entities stabilized by SiO₂.

In this study, the surface and textural properties as well as the catalytic performance of Ni/CeO₂ and NiIn/CeO₂ catalysts prepared by wet impregnation (WI) and deposition–precipitation (DP) are investigated. The addition of Ni (3.0 wt.%) resulted in a decrease in the specific surface area and pore volume in the case of the WI method, possibly due to a blockage of mesopores. A minimal addition of In (0.25 wt.%) caused a further decrease in the surface area in both cases. XRD analysis showed that Ni deposited on CeO₂ by DP resulted in some lattice incorporation, affecting the crystallinity of the support. The H₂-TPR profiles altered depending on the different ways of Ni and In introduction. STEM-EDS-derived elemental maps indicated that the Ni and NiIn particles deposited on CeO₂ using the DP method were somewhat smaller than in the WI synthesis. A comprehensive CO-DRIFTS analysis proved a direct Ni-In interaction in bimetallic samples, leading to the formation of a surface NiIn alloy. Ni/CeO₂ catalysts showed a higher activity in the process of dry reforming of methane (DRM) than the bimetallic counterparts at 650 °C, with the Ni_DP sample performing slightly better. However, the Ni_DP catalyst showed significant coking, which was drastically reduced by the addition of In. The agglomeration of Ni and/or NiIn particles during the 6 h DRM reaction somewhat impaired the catalyst performance. Overall, this study highlights the intricate relationship between the catalyst preparation, surface properties and catalytic performance in the DRM reaction and emphasizes the beneficial role of In addition in reducing the coking of the monometallic catalyst and the critical location and surface morphology of nickel nanoparticles decorated with indium and in contact with ceria.

Plasmonic metallic nanoparticles, like Au, can be used to tune the optical properties of photonic nanoarchitectures occurring in butterfly wing scales possessing structural color. The effect of the nanoscale Au depends on the location and the amount deposited in the chitin-based photonic nanoarchitecture. The following three types of Au introduction methods were compared regarding the structural and optical properties of the resulting hybrid bio-nanocomposites: (i) growth of Au nanoparticles inside the nanopores of butterfly wing scales by a light-induced in situ chemical reduction of HAuCl₄ in aqueous solution containing sodium citrate, as a new procedure we have developed, (ii) drop-drying of the aqueous Au sol formed during procedure (i) in the bulk liquid phase, and (iii) physical vapor deposition of Au thin film onto the butterfly wing. We investigated all three methods at two different Au concentrations on the wings of laboratory-bred blue-colored male Polyommatus icarus butterflies and characterized the optical properties of the resulting hybrid bio-nanocomposites. We found that the drop-drying and the in situ growth produced comparable redshift in the spectral position of the reflectance maximum associated with the chitin-based photonic nanoarchitecture in the wing scales, while the 5 nm or 15 nm thick Au layers vacuum deposited onto the butterfly wing behaved like an optical filter, without inducing spectral shift. The in situ growth in the photonic nanoarchitecture under intense illumination produced uniform Au nanoparticles located in the pores of the biological template, which is more advantageous for further applications. An additional benefit of this method is that the Au nanoparticles do not aggregate on drying, like in the case of drop-drying of preformed Au nanoparticles from the citrate-stabilized sol.