Transition-Metal-Doping of CaO as Catalyst for the OCM Reaction, a Reality Check

Abstract

In this study, first-row transition metal-doped calcium oxide materials (Mn, Ni, Cr, Co., and Zn) were synthesized, characterized, and tested for the OCM reaction. Doped carbonate precursors were prepared by a co-precipitation method. The synthesis parameters were optimized to yield materials with a pure calcite phase, which was verified by XRD. EPR measurements on the doped CaO materials indicate a successful substitution of Ca2+ with transition metal ions in the CaO lattice. The materials were tested for their performance in the OCM reaction, where a beneficial effect towards selectivity and activity effect could be observed for Mn, Ni, and Zn-doped samples, where the selectivity of Co- and Cr-doped CaO was strongly reduced. The optimum doping concentration could be identified in the range of 0.04-0.10 atom%, showing the strongest decrease in the apparent activation energy, as well as the maximum increase in selectivity.

Nickel-Doped CaO to Improve Its Antisintering Property and Electron-Transfer Ability for the Removal of As2O3 from Flue Gas: Experiments and DFT Simulations

“…However, when the doping amount is increased, the atomic spacing of the dopant is shortened, which reduces the doping effect. 27 Therefore, the Ni-modified CaO adsorbent can enhance its surface electron-transfer ability and sintering resistance to some extent. However, nothing is known about how Ni affects the microscopic process of As 2 O 3 adsorption on CaO.…”

“…In addition, it was discovered that the doping of trace amounts of nickel in CaO significantly improves its electronic characteristics and the redox capacity of the adsorbed molecules. However, when the doping amount is increased, the atomic spacing of the dopant is shortened, which reduces the doping effect …”

Surfactant-Capped Silver-Doped Calcium Oxide Nanocomposite: Efficient Sorbents for Rapid Lithium Uptake and Recovery from Aqueous Media

“…It has been observed that the performance of CaO is improved by doping it with different materials and transition metals (e.g., Ag, Ni, etc.) [35,36]. This is because the introduction of dopants creates new states in the oxide gap, which improves its performance.…”

Atomically Dispersed Platinum in Surface and Subsurface Sites on MgO Have Contrasting Catalytic Properties for CO Oxidation

“…The observation of atomically dispersed platinum atoms not only in the first MgO layer but also in the second layer calls to mind reports of atomically dispersed supported metals in which the metals have been regarded as support-embedded. − The literature includes many examples of doped solid catalysts, with dopants in various and difficult-to-determine subsurface sites. , The term embedded commonly implies substitution of an additive or doped metal into sites such as cation vacancies of supports typified by metal oxides, but this term is vague because the substitution can occur both at the surface and within the bulk of the support …”

“…37−39 The literature includes many examples of doped solid catalysts, with dopants in various and difficult-todetermine subsurface sites. 40,41 The term embedded commonly implies substitution of an additive or doped metal into sites such as cation vacancies of supports typified by metal oxides, 37 but this term is vague because the substitution can occur both at the surface and within the bulk of the support. 42 The Journal of Physical Chemistry Letters Some prior catalysis investigations acknowledge that subsurface platinum could contribute to reactivity, but the authors did not explicitly consider these sites in models (e.g., ref 43).…”