Comparing the Performance of Various Activated Carbon (AC) Based Catalysts

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.

Study Results

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]

Reference

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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