Elsevier

Catalysis Communications

Volume 3, Issue 8, August 2002, Pages 327-333
Catalysis Communications

Novel nitrogen containing heterogeneous catalysts for oxidative dehydrogenation of light paraffins

https://doi.org/10.1016/S1566-7367(02)00141-3Get rights and content

Abstract

Novel nitrogen contained catalyst CoNx/Al2O3 yielded high performance in the oxidative dehydrogenation of propane and n-butane. 47.6 and 37.4 wt% yield of olefins at 82% butane and 76.7% propane conversion were measured at 600 °C. Ethylene and propylene were mainly formed at >400 °C via oxidative cracking of paraffins. XRD and XPS studies of the novel catalytic system indicate an essential modification of cobalt by nitrogen.

Introduction

Oxidative dehydrogenation of light alkanes to olefins provides a viable alternative to commercial processes of catalytic dehydrogenation and steam cracking. There are no chemical equilibrium limitations as in dehydrogenation processes and it does not require high temperature and high heat fluxes needed in steam cracking. Reported studies with different catalysts did not achieve yield of olefins from propane above 30 wt% [1], [2], [3], [4], [5], [6], [7]. Only high temperature thermal conversion of paraffins yielded about 35% of olefins [8]. Recent results obtained in oxidative dehydrogenation of n-butane on alumina supported cobalt oxide catalyst indicate efficiency of these catalytic systems for production of ethylene and propylene. Low temperature performance of catalysts in oxidative cracking on n-butane at 550 °C yielded 23% of olefins C2–C3 at 30 wt% total yield of olefins [9]. Enhanced cracking activity was explained by the increase of mobile oxygen share in active species [9] that is a key factor in oxidation processes. Therefore improvement of cobalt catalyst performance requires a further promotion of mobile oxygen share.

Cobalt porphyrins and phthalocyanines have been used as precursors for preparation of carbon supported cobalt catalysts that displayed high activity in reduction of molecular oxygen at low temperature in fuel cells [10], [11]. These samples were prepared by deposition of cobalt phthalocyanine on active carbon followed by heat treatment at 650–700 °C in an inert atmosphere forming Co–N structure.

The object of the present study was the preparation, characterization and testing of a novel cobalt catalyst for oxidative dehydrogenation of light paraffins.

Section snippets

Experimental and methods

Catalytic performance of catalysts was studied in the experimental rig consisting of a stainless tubular preheater and reactor in series, 17 mm ID and 250 mm long with 5.5 mm axial thermowell. Electric tapes controlled by Eurotherm heated the reactor and preheater. 1–4 g catalyst (extrudates 1.5 mm in diameter and 2–3 mm length) diluted with 4–12 g of inert SiC pellets to keep the reactor isothermal, was located between two layers of SiC particles of 3–4 mm in diameter. Total layer of catalyst

Results and discussion

Experimental results depicted in the Table 2 indicate that nitrogen promoted catalysts 1 and 2 were significantly more active in oxidative dehydrogenation of propane and n-butane than non-promoted catalyst 3. Even at 400 °C, the conversion of propane was 24 mol% at 59 wt% of selectivity to olefins (sample 2). Increasing the temperature to 550 °C yielded 33 wt% olefins, significantly higher than yield on non-promoted catalyst 3. Similar results were obtained for n-butane (samples 1–3).

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