Ni can be used as a catalyst for dry reforming of methane (DRM), replacing more expensive and less abundant noble metal catalysts (Pt, Pd, and Rh) with little sacrifice in activity. Ni catalysts deactivate quickly under realistic DRM conditions. Rare earth oxides such as CeO₂, or as CeO₂-ZrO₂-Al₂O₃ (CZA), are supports that improve both the activity and stability of Ni DRM systems due to their redox activity. However, redox-active supports can also enhance the undesired reverse water gas shift (RWGS) reaction, reducing the hydrogen selectivity. In this work, Ni on CZA was coated with an ultrathin Al₂O₃ overlayer using atomic layer deposition (ALD) to study the effects of the overlayer on catalyst activity, stability, and H₂/CO ratio. A low-conversion screening method revealed improved DRM activity and lower coking rate upon the addition of the Al₂O₃ ALD overcoat, and improvements were subsequently confirmed in a high-conversion reactor at long times onstream. The overcoated samples gave an H₂/CO ratio of ∼1 at high conversion, much greater than uncoated catalysts, and no evidence of deactivation. Characterization of used (but still active) catalysts using several techniques suggests that active Ni is in formal oxidation state >0, Ni-Ce-Al is most likely present as a mixed oxide at the surface, and a nominal thickness of 0.5 nm for the Al₂O₃ overcoat is optimal.

Low- and high-density polyethylene (LDPE/HDPE) have been selectively depolymerized, without added H₂, to C2–C20 + alkanes/alkenes via energy-efficient radio frequency induction heating, coupled with dual-functional heterogeneous Fe₃O₄ and Ni- or Pt-based catalysts. Fe₃O₄ was used to locally generate heat when exposed to magnetic fields. Initial results indicate that zeolite-based Ni catalysts are more selective to light olefins, while Ni supported on ceria catalysts are more selective to C7–C14 alkanes/alkenes. LDPE conversions up to 94% were obtained with minimal aromatic, coke, or methane formation which are typically observed with thermal heating. Two depolymerization mechanisms, a reverse Cossee–Arlman mechanism or a random cleavage process, were proposed to account for the different selectivities. The depolymerization process was also tested on commercial LDPE (grocery bags), polystyrene, and virgin HDPE using the Ni on Fe₃O₄ catalyst, with the LDPE resulting in similar product conversion (∼48%) and selectivity as for virgin LDPE.

The assembled state of nanoparticles (NPs) within porous matrices plays a governing role in directing their biological, electronic, and catalytic properties. However, the effects of the spatial confinement and environmental factors, such as salinity, on the NP assemblies within the pores are poorly understood. In this study, we use adsorption isotherms, spectrophotometry, and small-angle neutron scattering to develop a better understanding of the effect of spatial confinement on the assembled state and catalytic performance of gold (Au) NPs in propylamine-functionalized SBA-15 and MCM-41 mesoporous silica materials (mSiO₂). We carry out a detailed investigation of the effect of pore diameter and ionic strength on the packing and spatial distribution of AuNPs within mSiO₂ to get a comprehensive insight into the structure, functioning, and activity of these NPs. We demonstrate the ability of the adsorbed AuNPs to withstand aggregation under high salinity conditions. We attribute the observed preservation of the adsorbed state of AuNPs to the strong electrostatic attraction between oppositely charged pore walls and AuNPs. The preservation of the structure allows the AuNPs to retain their catalytic activity for a model reaction in high salinity aqueous solution, here, the reduction of p-nitrophenol to p-aminophenol, which otherwise is significantly diminished due to bulk aggregation of the AuNPs. This fundamental study demonstrates the critical role of confinement and dispersion salinity on the adsorption and catalytic performance of NPs.