The performance of different activated carbon (AC) based catalysts in the reforming of CH4 with CO2 was compared in this study. The AC-based catalysts studied were raw AC, AC modified with NaNO3 (designated as AC-NaNO3), and AC modified with HNO3 (designated as AC-HNO3).
Performance Comparison Study
A fixed-bed reactor was used to perform CH4-CO2 reforming experiments at temperatures of 700-1000°C. Techniques such as temperature programmed oxidation-CO2 (TPO-CO2), CO2 chemisorption, Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) were used for the characterization of the catalysts.
The catalysts showed significantly different catalytic activities at low temperatures, but had similar catalytic activity at elevated temperatures. CH4 and CO2 were converted by 17.7% and 29.7%, respectively, on an average, when AC-NaNO3 was used at 700°C. The values are 2.4 and 3.2 folds greater than those over AC. However, CH4 and CO2 conversions were beyond 90% at 1000°C for all catalysts.
Additionally, there was an increase in the mole ratio of H2/CO with temperature in all cases. The mole ratio of H2/CO over AC-HNO3 varies between 0.76 and 0.94 at different temperatures, much closer to 1 when compared to the other two catalysts.
The characterization results revealed the key role played by NaNO3 in the creation of mesopores and surface oxygenated groups as well as in the reduction of deposited carbon. Hydroxyl group is more instrumental in CH4-CO2 reforming.
TPO-CO2 observations revealed the formation of two types of deposited carbon during the reforming reaction. The apparent activation energies catalyzed by AC, AC-HNO3, and AC-NaNO3 in the CH4-CO2 reforming reactions were 202, 227, and 123kJ/mol, respectively.
The same TA in conjunction with HPR-20 QIC TMS, a mass spectrometer from Hiden Analytical, was used to perform TPO-CO2 of the used catalyst (Figure 1). At a heating rate of 5°C/min, the used catalyst was heated from room temperature to 1200°C in 100ml/min CO2. The online MS was used to measure the CO generated with an electron ionization voltage of 0-220eV.
Figure 1. TPO-CO2 profiles of the used catalysts [catalyst weight: 0.3g; inlet flow rate: 20ml/min; inlet CH4:CO2 mole ratio: 1; temperature: 900°C; reaction time: 240min]
Project Summary by: Maohong Fan Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA
Paper Reference: L. Xu et al. (2014) “Catalytic CH4 reforming with CO2 over activated carbon based catalysts” Applied Catalysis A: General 469, 387-397
Hiden Product: HPR-20 QIC TMS Transient MS
This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.
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