(3av) O2-Assisted Dry Reforming of Methane on the Al2O3 Supported Ni-Co Catalyst

Dry reforming of methane (DRM) has been extensively studied as a way to decrease the impact of greenhouse gases (CO₂ and CH₄) on the environment by converting them into syngas (a mixture of CO and H₂). Non-noble metal based catalysts are generally used because of their low cost. Furthermore, supported nickel-cobalt catalysts of specific Ni:Co ratio are more active than supported nickel catalysts. However, these catalysts suffer from deactivation due to coke formation and sintering. O₂ addition to the DRM reactants, referred to as ODRM, could be a useful strategy to enhance the activity and suppress carbon formation.

In this study, Al₂O₃ supported 10% (w/w) Ni-Co catalyst was prepared by the incipient wet impregnation method with the molar ratio of Ni:Co of 3:1. The catalyst was calcined at 500 and 850°C and referred to as Ni₃Co500 and Ni₃Co850. The catalyst was characterized by H₂-TPR, XRD, BET, UV-vis, H₂-chemisorption and XPS. A quartz tube downward flow packed bed reactor was used for the reactions. All the reactions were performed at 600 and 750°C, and at atmospheric pressures, with a space-velocity (GHSV) of 36000 ml/g_cat-h. The molar feed composition was maintained at CH₄:CO₂:O₂:N₂ = 1:1:x:1-x, where x was 0 and 0.225 for DRM and ODRM, respectively. The spent catalysts were also characterized.

The H₂-TPR profile reported in Figure 1 showed the reduction profile of both the catalysts in H₂ environment. The reduction of Ni₃Co850 occurred at a relatively higher temperature than Ni₃Co500, which appeared to be due to a strong metal-support interaction. The H₂-chemisorption data suggests that the effective dispersion of the active metals on reduced Ni₃Co500 and Ni₃Co850 was 4.4 and 1.4%, respectively. The activity results averaged over 4 h of time-on-stream are reported in Table 1. The Ni₃Co500 showed higher CH₄ conversion at both the reaction temperature, which is consistent with its higher dispersion. At 750°C, both the catalyst showed an increase in CH₄ and CO₂ conversions, which were close to equilibrium values. The H₂/CO ratio increased significantly during ODRM and reached values close to 1. The maximum attained H₂/CO ratio was 0.92 ± 0.07 for the Ni₃Co500 catalyst at 600°C. Furthermore, the carbon deposited decreased by adding O₂ and/or increasing the temperature. However, the CO₂ conversion decreased with O₂ addition.

The ODRM reaction provided higher CH₄ conversion and H₂/CO ratio than the DRM reaction. The O₂ assisted DRM removed the carbon deposition problem. Moreover, the activity results of DRM reveal that the strong metal-support interaction in Ni₃Co850 provided better carbon suppression results.

Research Interests

The increasing energy demand creates the need to develop the alternate energy resources in the present world. Synthesis gas must be a useful component to achieve such an emerging energy requirement. As the synthesis gas generation was pivotal in my M.Tech project (Steam reforming of glycerol using heterogeneous catalyst) and the PhD project (Advancements in dry reforming of methane on Ni-based catalysts to syngas), I have developed my interest towards synthesis gas generation and utilization. The synthesis gas generation by hydrocarbon reforming attracted many researchers in the past years. Glycerol is a by-product in the biodiesel industry and an economical feed for the synthesis gas production. Additionally, excessive fossil fuel consumption causes greenhouse gas emission that harms the environment due to global warming. Synthesis gas production techniques have been explored since its utility in the production of fertilizer, methanol, and other valuable chemicals. Dry reforming of methane (DRM) is studied as an eco-friendly synthesis gas generation technique as compared to industrially mature steam reforming of methane (SRM) technique. The conversion of two prime greenhouse contributors (CH₄ and CO₂) without the utilization of H₂O could be possible with the DRM reaction. However, the catalyst deactivation due to carbon deposition and high-temperature requirements are the major resistances in DRM process development. So, a highly active and carbon resistant catalyst development would make a useful contribution to the DRM research field. Auto-thermal reforming is an effective process integration in terms of maintaining catalyst stability by carbon removal. The parallel occurrence of partial oxidation of methane (POM) with DRM or SRM makes the Auto-thermal reforming an energy-efficient process. Due to the influencing advantages of synthesis gas, my future attempts would be as follows.

1. The development of an economic catalyst for the DRM. The Ni-based catalysts are cost-efficient and active for the DRM reaction but associated with carbon deposition problems. Identifying and evolving the inherent qualities of the Ni-based catalysts would be a key goal during the catalyst development.
2. As the endothermic nature of the DRM reaction hampers its industrial appreciation, the exothermic Partial Oxidation of Methane (POM) and the Auto-thermal reforming have the potential possibilities to explore.
3. Tri reforming of methane (a combination of SRM, DRM and POM) would be an investigative approach to enhance the synthesis gas generation and alleviate the carbon deposition problem.
4. Among the several synthesis gas utilities, interest must be devoted to the online conversion of the produced synthesis gas by the methods mentioned above to the valuable chemicals through the Fischer-tropsch process.