X-ray diffraction and TGA kinetic analyses for chemical looping combustion applications

Synthesis and characterization of supported metal-based oxygen carriers were carried out to provide information related to the use of oxygen carriers for chemical looping combustion processes. The Cu, Co, Fe, Ni metals supported with Al2O3, CeO2, TiO2, ZrO2 were prepared using the wetness impregnation technique. Then, the X-ray Diffraction (XRD) characterization of oxidized and reduced samples was obtained and presented. The kinetic analysis using Thermogravimetric analyzer (TGA) of the synthesized samples was conducted. The kinetics of reduction reaction of all samples were estimated and explained.


Type of data
Images (x-ray, TGA kinetic calculations). How data was acquired

Value of the data
The data represent characterization of catalysts in term of different metal phases that existed during calcination and reduction experiments of metal-based oxygen carriers for CLC applications.
The data show essential calculations used to estimate the kinetics of metal-based oxygen carriers for methane fueled CLC process.
The data are useful for further studies on the development of kinetic models and determining the mechanism of reactions in the CLC process.

Data
The data present the XRD analysis of metal-based oxygen carriers for CLC applications. The data are Supplementary materials for the study describing the "Synthesis and study of metal-based oxygen carriers (Cu, Co, Fe, Ni) and their interaction with supported metal oxides (Al 2 O 3 , CeO 2 , TiO 2 , ZrO 2 ) in a chemical looping combustion system" [1].
The XRD analysis of Co, Cu, Fe, Ni metals supported with Al 2 O 3 , CeO 2 , TiO 2 , ZrO 2 is shown in Figs The weight loss and gain during the CLC reaction in the TGA were recorded and analyzed to study the effect of temperature on the conversion of Cu, Co, Fe, and Ni samples. The conversion of the reduction reaction of all samples was calculated using the following equation:    where; m is the mass of sample at any time (g), m r is mass of the reduced sample (g); and, m o is the mass of the oxidized sample (g). The conversion profiles during the reduction reaction showed no specific trend for all samples. However, a kinetic model that was developed by Gomez and Mahinpey [2] could be used to estimate the kinetic parameters of the reduction reaction. Considering that the surface reaction was the controlling step; hence, the equation used [2]: where; t X is residence time (min); X is conversion (-); T is absolute temperature (K); G(X) is conversion dependent function (-); k o is the frequency factor (1/min); E r is activation energy of reduction reaction (J/mol); and, R is the universal gas constant (J/mol K). If the reaction rate at a constant conversion is only a function of temperature, the following assumption applies [2]: The following graphs (Figs. 5-8) were generated for each sample to estimate Er and k o : All supported oxygen carriers exhibited an increase in the residence time as temperature decreased to achieve 50% solid conversion. Fast reduction profiles compared to other supported samples were noticed in the reduction reaction of all Cu-based oxygen carriers. As the temperature increased, the reaction rate increased but reduction time decreased. Similar reduction behaviour of Cu-based oxygen carriers was observed in the supported Co-based (Fig. 6), Fe-based (Fig. 7), and Nibased (Fig. 8) oxygen carriers. However, the reduction of Fe (Fig. 7) exhibited an additional resistant step that could be due to the deep reduction (i.e. phase transitions from FeO to Fe, Fe 2 O 3 to FeO and/or Fe 2 O 3 to Fe 3 O 4 ). The Cu/Al 2 O 3 sample showed a complete reduction time between 1 to 1.5 min during the first cycle of CLC, while other supported Cu samples with CeO 2 , TiO 2, and ZrO 2 showed a complete reduction time of more than 5 min The Co/Al 2 O 3 sample showed a complete reduction time of less Referring to Eq. (2), the slope in Figs. 5-8 represents the E r =R term in which the activation energy of the reduction reaction (E r ) was estimated by multiplying the slope with the universal gas constant. The intercept in Figs. 5-8 represents ln k o Â Ã term in which the frequency factor was estimated by taking the logarithmic inverse.

Experimental design, materials, and methods
The metal-based oxygen carriers were prepared using the incipient wetness impregnation method [3] at atmospheric pressure.
The following units were obtained beforehand and thoroughly cleaned:    The molar calculations performed based on the required percentage of both active metals and supports to determine the exact required mass. Then, in a beaker/magnetic stirrer, a 50 ml of DI water was added and the magnetic stirrer launched to a speed of 400-rpm. The appropriate amount of the metal nitrates obtained in a weighting paper and then carefully added to the beaker. The sample left to dissolve for 10 min. Next, a 100 ml of DI water was added to the beaker and the appropriate amount of the support oxides was weighted and carefully added to the beaker. The beaker was then covered and left stirred for 24 h at room temperature. Next, heating of the beaker started until the temperature of solution reached to 75°C. Most of water evaporated and the muddy sample was then collected into a ceramic bowl using a spatula. The sample dried in a conventional oven for 12 h at 120°C. Crushing of the dried samples using a ceramic mortar/bowl into a fine powder-like was accomplished. Finally, the dried sample calcined in air at 500°C for 3 h and reduced with hydrogen gas (50 ml/min) through a stainless-steel tubular reactor at 350°C for 3 h.
The X-ray diffraction (XRD) analysis was conducted using a Rigaku ULTIMA III X-ray diffractometer with Cu K-alpha radiation. The oxygen carriers scanned with 2-theta equal to 20-80, a 0.05°step, and a counting time of 2.0°per min, operating at 40 kV and 44 mA.