Mapping Temperature Heterogeneities during Catalytic CO₂ Methanation with Operando Luminescence Thermometry

Abstract

Controlling and understanding reaction temperature variations in catalytic processes are crucial for assessing the performance of a catalyst material. Local temperature measurements are challenging, however. Luminescence thermometry is a promising remote-sensing tool, but it is cross-sensitive to the optical properties of a sample and other external parameters. In this work, we measure spatial variations in the local temperature on the micrometer length scale during carbon dioxide (CO2) methanation over a TiO2-supported Ni catalyst and link them to variations in catalytic performance. We extract local temperatures from the temperature-dependent emission of Y2O3:Nd3+ particles, which are mixed with the CO2 methanation catalyst. Scanning, where a near-infrared laser locally excites the emitting Nd3+ ions, produces a temperature map with a micrometer pixel size. We first designed the Y2O3:Nd3+ particles for optimal temperature precision and characterized cross-sensitivity of the measured signal to parameters other than temperature, such as light absorption by the blackened sample due to coke deposition at elevated temperatures. Introducing reaction gases causes a local temperature increase of the catalyst of on average 6–25 K, increasing with the reactor set temperature in the range of 550–640 K. Pixel-to-pixel variations in the temperature increase show a standard deviation of up to 1.5 K, which are attributed to local variations in the catalytic reaction rate. Mapping and understanding such temperature variations are crucial for the optimization of overall catalyst performance on the nano- and macroscopic scale.

Spatiotemporal Heterogeneity of Temperature and Catalytic Activation within Individual Catalyst Particles

“…Figure a shows the three-dimensional (3D) reconstruction of NaYF 4 @SiO 2 distributed in the catalyst particle by the emission excited by a 980 nm laser at 623 K. As shown in Figure b, the focal plane of the catalyst particle was selected as a plane at z = 15 μm from the top. Recently, Jacobs et al measured spatial temperature distribution on supported metal catalysts (Ni/TiO 2 ) with the addition of a luminescent thermometer Y 2 O 3 :Nd 3+ by pixel-to-pixel mapping during CO 2 methanation. Under inert conditions, they found that the LIR of the luminescent thermometer vary spatially at a given temperature.…”

“…Implementing the upconversion spectrometer to detect the luminescence spectra of Yb 3+ ,Er 3+ -codoped NaYF 4 @SiO 2 nanoparticles adhered to the catalyst surface or mixed with the catalyst can obtain the local surface temperature of the individual catalyst or catalyst bed with transparent walls during hydrocarbon conversions . Spatially resolved detection of the upconversion luminescence (UL) spectra of Y 2 O 3 doped with Nd 3+ mixed in Ni/TiO 2 catalysts can obtain the local temperature of the catalyst surface during CO 2 methanation . In the methane oxychlorination reaction catalyzed by EuOCl, the fluorescence emission spectra of the catalyst material can also be used to operando determine the local surface temperature in the fixed-bed reactor .…”

“…However, the spatial resolutions of these thermometric techniques are limited to millimeters, restricting their applications for individual catalyst particles with sizes of industrial interest (∼microns). Luminescence thermometries, ,− which rely on the changes in adsorption or emission spectrum induced by temperature variations, provide a potential way for nonintrusive local temperature sensing with sufficient spatial and temporal resolution. For instance, the luminescence of lanthanide ions Er 3+ , Nd 3+ , or Eu 3+ in inorganic hosts excited by near-infrared light (980 or 785 nm) or UV light is temperature-dependent.…”

Dual Functional Materials: At the Interface of Catalysis and Separations

“…Localized heat transfer may also be important to consider and is an intriguing opportunity for further study. We hypothesize that the top performing DFMs use local thermal gradients during exothermic hydrogenation to facilitate desorption and reaction …”

“…We hypothesize that the top performing DFMs use local thermal gradients during exothermic hydrogenation to facilitate desorption and reaction. 28 Kinetic studies become more complicated when common flue gas contaminants are included in the experiments. Although simplified kinetic studies with clean and dry flue gas are helpful for measuring intrinsic kinetics, using more realistic simulated flue gas will help bridge the gap between academic and industrial studies, accelerating DFM implementation.…”