Original data of the article 'Effect of ZrO2 Crystal Phase on the Catalytic Performance of the Reverse Water-Gas Shift Reaction'

1 Experiment Section All chemicals and reagents for synthesis, including Zirconium nitrate (ZrO(NO3)2·xH2O), urea and methanol, were purchased from Aladdin Chemical, the chemical purity was Analytical Reagent and the chemicals were used without further purification. The reaction gases, including hydrogen (H2, 99.999%), carbon dioxide (CO2, 99.999%), nitrogen (N2, 99.999%), helium (He, 99.999%), argon (Ar, 99.999%), deuterium (D2, 99.999%) and a 13.3%CO2/53.3%H2/33.4%Ar mixture, were supplied by Taiyuan Taineng Gas Co., Ltd. and used as received without further purification. Deionized water with a resistivity higher than 18.5 MΩ was used throughout the experiments. 1.1 Catalyst Preparationm-ZrO2 and t-ZrO2 were synthesized using the hydrothermal method[27,28]. As a typical synthesis method, to synthesize m-ZrO2, 9.26 g of ZrO(NO3)2·xH2O was placed in a 200 mL Teflon-lined vessel, 80 mL of deionized water was added, and the mixture was vigorously stirred until completely dissolved. Then, 24.08 g of urea was added, and stirring was continued for 0.5 h. The synthesized gel was transferred to a stainless steel autoclave and held at 190 °C under static conditions for 32 h. The resulting precipitate was washed four times with deionized water by centrifugation and then dried at 110 °C for 12 h. Finally, the ground catalyst was calcined at 400 °C for 4 h with a heating rate of 2 °C min-1. t-ZrO2 can be synthesized using methanol as the solvent and following the same synthesis procedure as for m-ZrO2. 1.2 Characterization of the CatalystsPowder X-ray diffraction (XRD) patterns of the m-ZrO2, t-ZrO2, and c-ZrO2 catalysts were conducted on a Bruker D8 Advance diffractometer with a nickel-filtered Cu Kα (λ = 0.15418 nm) radiation source operated with an operation voltage of 40 kV and an operation current of 50 mA, the test range is 5-90°. The ZrO2 phase is determined by comparing the diffraction pattern with the PDF card data in the Joint Committee on Powder Diffraction Standards (JCPDS) database.Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) of the m-ZrO2, t-ZrO2, and c-ZrO2 catalysts were acquired on a JEM-2100F high resolution transmission electron microscope with an operation voltage of 200 kV. The samples were dispersed in ethanol and then placed on an extra-thick carbon film for analysis.In a liquid nitrogen environment (-196 °C), the structural properties of the sample were measured using the Jingwei Gaobo JW-BK 200 specific surface area and pore size analyzer. The specific surface area was determined by the Brunauer–Emmett–Teller (BET) method. Before testing, the catalyst was degassed under vacuum at 200 °C for 5 hours.Electron Paramagnetic Resonance (EPR) spectroscopy of various m-ZrO2, t-ZrO2, and c-ZrO2 catalysts were recorded at -129 °C on a JEOL JESFA200 ESR spectrometer (9.087 GHz) at a modulation frequency of 100 kHz, a microwave power of 0.998 mW, and a modulation amplitude of 0.35 mT. Before testing, the samples were treated in a glove box under four atmospheres of Ar, H2, CO2, and CO2+H2 (13.3% CO2/53.3% H2/33.4% Ar) for 1 hour, with a treatment temperature of 450 ℃ and a gas flow rate of 30 mL min-1.Quasi in situ XPS experiments of the m-ZrO2, t-ZrO2, and c-ZrO2 catalysts were conducted on an ESCALAB 250Xi spectrometer equipped with a reaction chamber using a monochromatic Al anode Kα radiation (1486.6 eV) as the excitation source. Prior to the measurements, the samples were pretreated in a glove box under atmosphere of N2 with a flow rate of 30 mL min-1 at 450 °C for 1 h. Subsequently, the samples were directly transferred into analysis chamber for XPS measurements without exposure to air. The likely charging of sample was corrected by fixing the binding energy of the adventitious carbon (C1s) to 284.8 eV.H2-D2 exchange and CO2 temperature-programmed desorption (CO2-TPD) experiments were conducted on a self-built fixed reactor coupling with an online HIDEN QIC-20 gas phase mass spectra (MS). For the H2-D2 exchange measurement, 100 mg of m-ZrO2, t-ZrO2, or c-ZrO2 catalyst was subjected to in situ treatment under an Ar atmosphere with a flow rate of 30 mL min-1 at 450 °C for 0.5 h and then cooled down to RT naturally in Ar atmosphere. Afterwards, the gas was switched to a mixed atmosphere containing 5% H2 and 5% D2 balanced with Ar with a total flow rate of 31.5 mL min-1 at RT. The outlet gases containing HD (m/z =3), H2 (m/z =2), and D2 (m/z =4) were recorded by the MS.For the CO2-TPD measurement, 100 mg of m-ZrO2, t-ZrO2, or c-ZrO2 catalyst was in situ purged in Ar with a flow rate of 30 mL min-1 at 450 °C for 0.5 h. Next, the sample was cooled down to RT naturally. Pure CO2 was subsequently introduced into the system with a flow rate of 30 mL min-1 at RT for 1 h till to saturation. Finally, the sample was purged by pure Ar with a flow rate of 30 mL min-1 at 450 °C for 0.5 h and then heated to 600 °C at a heating rate of 5 °C min-1. The desorbed CO2 (m/z =44) signal was recorded by the MS.In situ diffuse reflectance infrared Fourier transformed spectroscopy (DRIFTS) experiments were performed on a Nicolet iS50 FT-IR spectrometer equipped with an in situ high-temperature reaction cell (Harrick Scientific Products, Inc.) in series mode with 256 scans and a resolution of 4 cm-1 with an MCT/A detector. For in situ DRIFTS measurement of the stepwise reactions of first CO2, then CO2 + H2, and finally H2, 100 mg of m-ZrO2, t-ZrO2, or c-ZrO2 catalyst was purged by pure Ar with a flow rate of 30 mL min-1 at 450 °C for 0.5 h, and then heated to 500 °C and stabilized for 10 min, whose spectra were taken as the background spectra. Then, 13.3% CO2 balance with Ar with a flow rate of 30 mL min-1 for 0.5 h at 500 °C and the time-resolved DRIFTS spectra were collected for 0.5 h until saturation. Afterwards, 53.3% H2 was introduced in the presence of CO2 (CO2:H2 = 1:4) balance with Ar with a total flow rate of 30 mL min-1 and corresponding time-resolved DRIFTS spectra were collected for another 0.5 h until stability. Finally, CO2 was withdrawn to keep a 53.3%/H2 balanced with Ar atmosphere with a total flow rate of 30 mL min-1 at 500 °C, simulating surface carbonaceous species hydrogenation reaction, whose time-resolved DRIFTS spectra were collected for another 0.5 h. 1.3 Catalytic Performance Evaluations and Kinetic MeasurementsCO2 hydrogenation to CO reaction was conducted in a fixed bed reactor using the reaction gas consisted of 13.3% CO2 and 53.3% H2 (CO2:H2 = 1:4) balanced with He with a total flow rate of 30 mL min-1. Prior to measurement, 100 mg of m-ZrO2, t-ZrO2, or c-ZrO2 catalyst was placed in quartz tube and loaded into the fixed-bed reactor. Afterwards, reaction gas was introduced and the sample was heated to the desired temperature at a ramp rate of 5 °C min-1 and then held for 50 min until the reaction reached a steady state. The composition of the gases after the reaction was analyzed using an on-line gas chromatography (FULI 9790 Plus) equipped with a TCD detector and a flame ionization detector (FID). The CO2 conversion was calculated on basis of the change in concentrations of the inlet and outlet gases CO2 (Eq. 1). The product selectivity was calculated from the ratio of individual products to total products (Eq. 2). The carbon balance was taken into account in our system.   Conversion.CO2=(nCO2,in – nCO2,out)/nCO2,in                                  (Eq. 1)SelectivityCH4orCO=nCH4orCO/(nCH4+nCO)                                 (Eq. 2)Reaction orders of H2 or CO2 were conducted at 400 °C using the same procedures as the activity measurement. All CO2 conversions were controlled below 15% without the thermodynamic equilibrium and mass transfer limitations. Reaction order of H2 was acquired by keeping the CO2 pressure at 12.1 kPa and changing the H2 pressure from 27.5 kPa to 55.5 kPa. Reaction order of CO2 was acquired by keeping the H2 pressure at 55.5 kPa and changing the CO2 pressure from 6.1 kPa to 12.1 kPa.