Elsevier

Materials Letters

Volume 221, 15 June 2018, Pages 18-21
Materials Letters

Ni-MOx-Al2O3 (M = Mg, Cr, Ce) catalysts prepared by Pechini technique for low temperature steam reforming of light hydrocarbons into methane-rich gas

https://doi.org/10.1016/j.matlet.2018.03.010Get rights and content

Highlights

  • Ni-MOx-Al2O3 (M = Mg, Cr, Ce) catalysts prepared by Pechini technique.

  • Low temperature steam reforming of propane-methane mixture into methane-rich gas.

  • Ni-MgO-Al2O3 exhibited the highest activity.

  • The effect was attributed to Ni-MgO interaction, which enhanced Ni dispersion.

Abstract

30 wt.% NiO – 20 wt.% MOx-Al2O3 (M = Mg, Cr, Ce) catalysts with highly disordered structure were prepared by Pechini technique. Reduced catalysts were tested in low temperature steam reforming of model propane-methane mixture into methane-rich gas. The catalysts were compared with industrial samples and exhibited appropriate activity which increased in the following order: Industrial CH4 reforming catalyst < Ni-CeO2-Al2O3 ≈ Ni-Cr2O3-Al2O3 ≈ Ni-Al2O3 < Ni-MgO-Al2O3 ≈ Industrial CO and CO2 methanation catalyst. Ni-MgO-Al2O3 catalyst with lower Ni content and higher calcination and reduction temperatures showed activity close to that of industrial methanation catalyst. The effect was attributed to Ni-MgO interaction which resulted in higher Ni dispersion.

Introduction

Nowadays many gas-and-oil producing companies among the world and especially in Russia, Nigeria, Saudi Arabia and north states of USA face the problem of associated petroleum gas (APG) and shale gas utilization. Very often, APG, as well as high-caloric natural gas (HCNG), are wasted in flare installations due to deficient transport and refinery infrastructure. APG and HCNG have variable composition (vol.%, 50–70 CH4, 5–10 C2H6, 5–15 C3+-hydrocarbons, 1–10 N2, 1–10 CO2) and can neither be pumped to pipelines due to high dew point temperature nor directly used as a fuel for internal combustion engines (ICE) due to high calorific effect and detonation risk. Traditional gas refinery technologies are economically inefficient for low-debit and distant oil and gas fields. Therefore, there is a need for alternative methods for on-site processing of APG and HCNG. Low temperature steam reforming (LTSR) of C2+-hydrocarbons [1], [2], [3] is considered as one of the promising alternatives. As a result of this process, the volume of the gas mixture increases and the mixture is enriched with methane due to C2+-hydrocarbons conversion by the reaction:CnH2n+2+n-12H2O3n+14CH4+n-14CO2n2

The reaction is performed under pressure 1–20 bar, at temperature 250–350 °C and molar ratio H2O/C < 1 over Ni-based catalysts [1], [2], [3]. Such conditions provide high methane content in the reaction products, high energy-efficiency by reducing heat supply required for water evaporation, but suffers from possible catalyst coking. Overall process (1) combines endothermic reactions of hydrocarbons steam conversion and exothermic reactions of CO2 methanation and hydrocarbons hydrogenolysis. Depending on the composition of the initial feed and reaction kinetics, the reaction temperature profile could be non-uniform assuming local hot spots with T > 400 °C in case of adiabatic reactor.

There are two types of industrial catalysts that could be applied for LTSR of light hydrocarbons: pre-reforming/reforming catalysts with high thermal stability, Ni content of 10–15 wt.% and operational temperatures 400–550/700–900 °C and carbon oxides methanation catalysts with low thermal stability, high Ni content up to 60 wt.% and operational temperatures of 200–300 °C [4], [5], [6]. It should be noted, that there are no catalysts combining high activity at low temperatures and sufficient thermal stability. Therefore, design of Ni-based catalysts for LTSR reaction is a breakthrough task. Different types of oxide dopants were proposed to promote Ni dispersion (Cr2O3 [4]), activity (MgO [7]) and coking resistance (CeO2 [8]) of Ni-based reforming and methanation catalysts. However, there are no data on the influence of these oxides on the performance of Ni-based catalysts in LTSR of light hydrocarbons.

In the present paper we report the structural characterization of Ni-MOx-Al2O3 (M = Mg, Cr, Ce) catalysts prepared by Pechini technique, as well as their catalytic properties in LTSR of propane-methane mixture as a model of APG. To the best of our knowledge, this is the first report on such catalysts testing in LTSR reaction.

Section snippets

Experimental

Nickel-alumina (Ni-Al) catalysts modified with Cr2O3 (Ni-Cr-Al), CeO2 (Ni-Ce-Al), MgO (Ni-Mg-Al) were prepared by well-known Pechini technique [9], [10] using metals nitrates, citric acid and ethylene glycol at molar ratio of 1:1:1. The polymeric precursor formed after water evaporation at 120 °C was calcined at 600 °C for 6 h. The content of NiO and MOx (M = Mg, Cr, Ce) in the prepared catalysts was set to 30 and 20 wt.%, respectively.

NIAP-07-05 industrial methanation catalyst (Ni-meth) with

Results and discussion

Fig. 1 presents the effect of temperature on C3H8, CH4 and CO2 concentrations (on dry basis) for LTSR of propane-methane mixture over Ni-Al, Ni-Cr-Al, Ni-Ce-Al, Ni-Mg-Al, Ni-meth and Ni-ref catalysts together with the temperature dependencies of equilibrium concentrations. All the catalysts demonstrated dependencies of the same type: with the temperature raise [C3H8] decreases to a value close to zero (Fig. 1a), which corresponds to equilibrium; [CH4] increases, reaches a maximum, and then

Conclusions

30 wt.% NiO – 20 wt.% MOx-Al2O3 (M = Mg, Cr, Ce) catalysts with highly disordered structure were prepared by Pechini technique. Reduced catalysts were tested in low temperature steam reforming of a model propane-methane mixture into methane-rich gas. Ni-Al2O3, Ni-CeO2-Al2O3, Ni-Cr2O3-Al2O3 catalysts exhibited intermediate activity between industrial natural gas steam reforming and methanation catalysts. Ni-MgO-Al2O3 showed activity close to that of industrial methanation catalyst. The effect

Acknowledgements

The reported study was funded by RFBR and Government of the Novosibirsk region according to the research project № 17-43-543136 r_mol_a (S.I. Uskov) in the part of catalyst preparation and catalytic properties study. In the part of physical-chemical characterization the work was conducted within the framework of the budget project No. AAAA-A17-117041710088-0 for Boreskov Institute of Catalysis.

References (12)

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