Chemical-looping combustion (CLC) and chemical-looping reforming (CLR) involve the use of a metal oxide as an oxygen carrier which transfers oxygen from combustion air to the fuel. Two interconnected fluidized beds, a fuel reactor, and an air reactor are used in both processes. In the fuel reactor, the fuel is oxidized by a metal oxide, and in the air reactor, the reduced metal is oxidized back to the original phase. In CLC, a high conversion of the fuel to CO2 and H2O is required in the fuel reactor, whereas only a partial oxidation of the fuel is desired in CLR. Oxides of Ni, Cu, Fe, and Mn supported on SiO2 and MgAl2O4 were prepared by dry impregnation and investigated under alternating reducing and oxidizing conditions in a thermogravimetric analyzer at 800−1000 °C using fuel (10% CH4, 10% H2O, and 5% CO2) and oxidizing gas (5% O2). NiO and CuO supported on both SiO2 and MgAl2O4 showed very high reactivity. However, the reactivity of NiO/SiO2 decreased as a function of the cycle number at 950 °C but w...

Redox investigation of some oxides of transition-state metals, Ni, Cu, Fe, and Mn Supported on SiO2

Converting plastic waste into valuable products (syngas) is a promising approach to achieve sustainable cities and communities. Here, we propose for the first time to convert plastic waste into syngas via the Fe2AlOx-based chemical looping technology in a two-zone reactor. The Fe2AlOx-based redox cycle was achieved with the pyrolysis of plastic waste in the upper zone, followed by the decomposition and thermal cracking of hydrocarbon vapors, and the oxidation and water splitting in the lower zone (850 °C) enabled a higher carbon conversion (81.03%) and syngas concentration (92.84%) when compared with the mixed feeding process. The iron species could provide lattice oxygen and meanwhile act as the catalyst for the deep decomposition of hydrocarbons into CO and the accumulation of deposited carbon in the reduction step. Meanwhile, the introduced water would be split by the reduced iron and deposited carbon to further produce H2 and CO in the following oxidation step. A high hydrogen yield of 85.82 mmol/g HDPE with a molar ratio of H2/CO of 2.03 was achieved from the deconstruction of plastic waste, which lasted for five cycles. This proof of concept demonstrated a sustainable and highly efficient pathway for the recycling of plastic waste into valuable chemicals.

Sustainable and Highly Efficient Recycling of Plastic Waste into Syngas via a Chemical Looping Scheme.

A novel system of biomass for the generation of inherently separated syngas by combining chemical looping CO2-gasification and steam reforming process

Previous work on calcium ferrites showed they were able to convert syngas to hydrogen via chemical looping. The mixture of iron and calcium and their oxides has different thermodynamic properties than iron oxide alone. Here, the use of methane, an abundant fuel, is investigated as the reductant in chemical looping syngas production. In contrast to syngas-fueled cycles, the looping materials became more active with cycling using methane as the fuel. When reduced by methane, the looping material often showed a significant induction period, indicating that products of reduction (in particular metallic Fe) acted as a catalyst for further reduction. The behavior in a thermogravimetric analyzer (TGA) and a fluidized bed was comparable, i.e., no degradation with cycling. The reduced C2F appeared to be easily reformed when oxidized with CO2, and there was little evidence of bulk phase segregation. The improved kinetics on cycling was likely due to the separation of metallic Fe onto the surface. Using hydrogen to partially reduce C2F promotes the catalytic pyrolysis of methane.

Understanding the Behavior of Dicalcium Ferrite (Ca2Fe2O5) in Chemical Looping Syngas Production from CH4

Carbonyl sulfide (COS) generated from various chemical and metallurgical industry sectors has been receiving considerable attention due to its environmental impact and threat to production chains. The catalytic hydrolysis of COS has been considered an economic way for converting the unremovable COS into H₂S that subsequently can be easily removed through the mature wet or dry desulfurization process. Searching for an effective catalyst with stable activity is always crucial for COS hydrolysis. In this study, alkali-free ordered mesoporous Al₂O₃ with a larger pore size, incorporated with Ni, Cu, or Fe as an additive, and synthesized via a one-pot approach has been investigated for the catalytic hydrolysis of COS at low temperatures. It has been demonstrated that alumina with ordered mesoporous structures exhibits significant catalytic activity over COS hydrolysis whose activity improved further when incorporated with transition metals. More importantly, the enlargement of mesopore size for all the catalysts is critical for maintaining their catalytic performance. By optimizing the pore size and the type of additive, a highly active and stable catalyst of Ni-containing mesoporous Al₂O₃ with a large pore size has been established, which exhibits a long-term COS conversion above 95% and strong sulfur resistance. With the help of various characterization techniques, the details of the hydrolysis reaction, as well as the sulfur poisoning mechanism, have been revealed. It is envisaged that the synthesized catalyst of alkali-free ordered mesoporous Al₂O₃ holds great application potential for the catalytic hydrolysis of COS in practical industrial applications.

Zhihao Zhou

Papers

Catalysts of Ordered Mesoporous Alumina with a Large Pore Size for Low-Temperature Hydrolysis of Carbonyl Sulfide

Chemical looping co-conversion of CH4 and CO2 using Fe2O3/Al2O3 pellets as both oxygen carrier and catalyst in a fluidized bed reactor