Catalytic Steam Reforming of Toluene: Understanding the Influence of the Main Reaction Parameters over a Reference Catalyst

Abstract

Identifying the suitable reaction conditions is key to achieve high performance and economic efficiency in any catalytic process. In this study, the catalytic performance of a Ni/Al2O3 catalyst, a benchmark system—was investigated in steam reforming of toluene as a biomass gasification tar model compound to explore the effect of reforming temperature, steam to carbon (S/C) ratio and residence time on toluene conversion and gas products. An S/C molar ratio range from one to three and temperature range from 700 to 900 °C was selected according to thermodynamic equilibrium calculations, and gas hourly space velocity (GHSV) was varied from 30,600 to 122,400 h−1 based on previous work. The results suggest that 800 °C, GHSV 61,200 h−1 and S/C ratio 3 provide favourable operating conditions for steam reforming of toluene in order to get high toluene conversion and hydrogen productivity, achieving a toluene to gas conversion of 94% and H2 production of 13 mol/mol toluene.

Activity and Stability of Different Fe Loaded Primary Catalysts for Tar Elimination

“…This result is explained by the promotion of the reverse WGS reaction due to its exothermic nature. The same trend with temperature was observed in other studies of catalytic reforming of tar model compounds, with this effect being attributing to the exothermic nature of the WGS reaction [68,74].…”

Toluene Steam Reforming over Ni/CeZrO2—The Influence of Steam to Carbon Ratio and Contact Time on the Catalyst Performance and Carbon Deposition

“…The impressive reduction of carbon accumulation during SRT over Ni/CeZrO 2 can be observed at S/C = 4. Zhu et al [16], who studied the Ni/Al 2 O 3 catalyst in SRT, also noticed the decrease in coke formation when the S/C increased. According to their work, 0.29, 0.22 and 0.17 g of carbon deposited per 1 g of the catalyst after 5 h time-on-stream at S/C = 1, 2, and 3, respectively.…”

“…There are few factors that play a role in increased C deposition over Ni/Al 2 O 3 [16] and must be underlined here: (i) the Ni loading, which was 20 wt.%, i.e., twice as high as in the case of Ni/CeZrO 2 (this is very important since Ni is the site for C deposition), (ii) the support, which is not reducible, and unlike CeZrO 2 , does not provide the active oxygen species for suppressing carbon species, and (iii) the contact time as low as 1.6 × 10 −5 s (shorter contact times results in increased coke formation; t c in the present work is 0.36 s). Ni/Al2O3 [16] and must be underlined here: (i) the Ni loading, which was 20 wt.%, i.e., twice as high as in the case of Ni/CeZrO2 (this is very important since Ni is the site for C deposition), (ii) the support, which is not reducible, and unlike CeZrO2, does not provide the active oxygen species for suppressing carbon species, and (iii) the contact time as low as 1.6x10 −5 s (shorter contact times results in increased coke formation; tc in the present work is 0.36 s). Based on the obtained results, the reaction pathways for the formation of filamentous carbon during SRT over Ni/CeZrO 2 can be proposed (Figure 6).…”

“…The contribution of H2 (x) produced in SRT, WGS, and H2O dissociation over the Ni/CeZrO2 catalyst in the product gas from toluene steam reforming was calculated using equations (15)(16)(17) and is presented in Figure 9. • 100 [%] (15)…”

“…The impact of S/C was even more pronounced in the case of Ni/CeO 2 , over which CH 4 conversion increased from 40% at S/C = 1 to 89% at S/C = 2. Toluene, considered a model tar compound, was converted in the SR reaction over Ni/Al 2 O 3 [16]. The catalyst showed the highest toluene conversion and hydrogen yield with the lowest coke deposition at elevated temperatures (above 800 • C).…”