Magnetic Properties of Efficient Catalysts Based on La‐Doped Ceria‐Supported Nickel Nanoparticles for rWGS Reaction. Influence of Ni Loading

Abstract

to a few processes: syntheses of urea, salicylic acid, and polycarbonates, but these only correspond to a few percentage of the potential CO 2 suitable to be converted into chemicals and/or fuels. [1] Conversion of CO 2 into CO by catalytic hydrogenation has been recognized as one of the most promising processes for CO 2 utilization. Synthesis gas (syngas) could then be used to produce hydrocarbons or oxygenated hydrocarbons via Fischer-Tropsch reaction, as well as for the synthesis of methanol. This is a basic chemical for the production of synthetic fuels and polymers, whose importance is increased by the progressing shift in resources used in the petrochemical industry from crude oil to natural gas. The syngas reaction is a process in two steps, in which the first and essential is the reduction of CO 2 to CO with H 2 , or reverse water gas shift reaction (rWGS, CO 2 + H 2 ↔ CO + H 2 O), using renewable H 2 . This reaction is endothermic, being thermodynamically favored at high reaction temperatures and in excess of H 2 ; therefore, the use of an active-selective-stable catalyst under these conditions is imperative.Regarding the reaction mechanism, it has been widely reported that the reaction requires a bifunctional catalyst, consisting of a metal, which favors activation and dissociation of H 2 and a reducible oxide, promoting CO 2 adsorption and oxygen mobility in the lattice. The rate-determining step for the reaction depends on the catalyst composition and reaction conditions, being, at high temperature RWGS reaction: COO bond cleavage on Pt, Pd, and Cu, owing to the high barrier on the surfaces, while OH binding with H to form H 2 O is rate-determining on Co, Fe, Ru, Ni, and Rh. [2][3][4] Copper-based catalysts, the most studied for WGS reaction, have been also applied to the rWGS reaction; [5][6][7] however these systems are not suitable at high temperature because of their poor thermal stability. [7] As alternative, ceria-supported nickel and noble-metals catalysts have shown excellent catalytic performance in terms of activity, selectivity, and stability for RWGS reaction. [8][9][10] These supported metals present high ability for activation and dissociation of H 2 molecules, [7] being Ni preferred due to its lower prices compared to expensive noble metals. [11] Ceria is a suitable support due to their basic properties. [12] Moreover, theThe influence of Ni loading on Ce 0.9 La 0.1 O 1.95 -supported Ni catalysts for CO 2 reduction with hydrogen (reverse water gas shift reaction) is studied. The samples are prepared by solution combustion synthesis (SCS), leading to materials with high thermal resistance, purity, and crystallinity, consisting of metallic nickel nanoparticles supported on La-doped ceria. The study of the ferromagnetic Curie temperature (T C ) and magnetization cycles suggest that the Ni nanoparticles are superparamagnetic, exhibiting magnetic order at room temperature, with T C strongly dependent on the particle size; this spans from 1.9, up to 80 nm. The structural study from synchrotr...

Highly Active and Stable Ni/La-Doped Ceria Material for Catalytic CO2 Reduction by Reverse Water-Gas Shift Reaction

“…Spin-polarized DFT calculations were performed to gain insights into the roles of the metal and oxide phases of low-loaded nickel-ceria model catalysts in the activation of CO 2 as well as the H 2 dissociation and subsequent H diffusion that ultimately leads to the formation of CO and H 2 O. Previous experimental results , indicate that the system consists of nickel metal nanoparticles supported on a La-doped ceria with different degrees of reduction. We chose a flat Ni 4 cluster structure supported on the fully oxidized CeO 2 (111) and on the fully reduced Ce 2 O 3 (0001) surfaces as representative models of low-loaded ceria-supported nickel catalysts, which illustrate accurately many of the essential atomic-scale features that control the catalyst stability, electronic structure, and surface reactivity, as described below.…”

“…Among the possible methods to prepare these ceria-supported Ni catalysts, we have selected the solution combustion synthesis (SCS) method. Using a patented specific protocol that includes, among other conditions, a controlled ratio between fuel and metal precursors, a porous and finely particulate metal oxides materials with very high macroporosity and the formation of Ni particles in the metallic state are obtained. − These critical points help to promote heat and mass transport and prevent the formation of hot-spots during the catalytic reaction. A deep characterization using X-ray and neutron diffraction, Raman spectroscopy, in situ NAP-XPS, and electron microscopy, in combination with DFT calculations, was performed and correlated with the reaction performance, highlighting the key parameters that control reactivity.…”

Hydroxyapatite Derived from Salmon Bone As Green Ecoefficient Support for Ceria-Doped Nickel Catalyst for CO2 Methanation

“…However, these catalysts’ reduction temperatures are lower than those of the unmodified ones, indicating better metal phase dispersion because CeO 2 reduces the weakening of the NiO–support interaction and increases the ability to disperse NiO on the HA surface. Besides that, Figure b also shows that the ceria-doped catalysts have weak reduction signals above 600 °C; these reduction signals belong to the reduction process of the phases of NiO–CeO 2 interaction or surface CeO 2 in the doped catalysts . The content of the CeO 2 doping is low (4–8%), so the reduction signal is not high.…”

“…Besides that, Figure 7 b also shows that the ceria-doped catalysts have weak reduction signals above 600 °C; these reduction signals belong to the reduction process of the phases of NiO–CeO 2 interaction or surface CeO 2 in the doped catalysts. 43 The content of the CeO 2 doping is low (4–8%), so the reduction signal is not high. When compared to other catalysts, the maximum reduction peaks of 10Ni6Ce/HA are in the lowest temperature region.…”

Bismuth single atom supported CeO2 nanosheets for oxidation resistant photothermal reverse water gas shift reaction

“…Based on the efficient photothermal system, the catalyst has become the key to realizing applicable photothermal RWGS. Scientists have found that various non-precious metal based catalysts are active for RWGS, including Ni-, 15,16 Cu-, [17][18][19] In-, 20 and Co-based catalysts. 21 Because RWGS operates in a hydrogen rich environment, the metal species in those catalysts are metallic or in low oxidation state.…”