Abstract
In this report, for the first time, it has been observed that proton-conducting oxide BaZr0.1Ce0.7Y0.2O3−δ (BZCY) has significant promotion effect on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen. Renewable hydrogen can be used for ammonia synthesis to save CO2 emission. By investigating the operating parameters of the reaction the optimal conditions for this catalyst were identified. It was found that at 620 °C with a total flow rate of 200 mL min−1 and a H2/N2 mol ratio of 3, an activity of approximately 250 μmol g−1 h−1 can be achieved. This is ten times larger than that for the unpromoted Ni catalyst under the same conditions although the stability of both catalysts in the presence of steam was not good. The specific activity of Ni supported on proton-conducting oxide BZCY is approximately 72 times higher than that of Ni supported on non-proton conductor MgOCeO2. These promotion effects were suspected to be due to the proton conducting nature of the support. Therefore it is proposed that the use of proton conducting support materials with highly active ammonia synthesis catalysts such as Ru and Fe will provide improved activity of at lower temperatures.
Highlights
Ammonia, due to its important use as a fertiliser is mass produced at approximately 150 million tons per annum [1]
It was found that proton-conducting oxide BZCY has promotion effects on the catalytic activity towards ammonia synthesis
X-ray Diffraction (XRD) analyses In the XRD results shown in Fig. 1, it can be seen that there are some small peaks attributed to BaCO3 and Y-doped CexZr1ÀxO2 present for BaZr0.1Ce0.7Y0.2O3Àd before and after being mixed with the NiO; after reduction at 700 C in H2/N2 mixture (90%H2) for 4 h, these peaks are no longer present
Summary
Due to its important use as a fertiliser is mass produced at approximately 150 million tons per annum [1]. It is commonly accepted that the rate limiting step for the ammonia synthesis reaction is the dissociative adsorption of nitrogen the reaction could be limited by the N binding energy due to the Sabatier principle [24] This is shown in Eqs (2)e(8) below: N2 þ* 4N*2. It was discovered that ammonia could be produced from hydrogen and nitrogen in an electrochemical cell [7,26e35] This led Vasileiou E et al [36,37] to achieve the electrochemical synthesis of ammonia using a proton conducting electrolyte. The effects of a similar proton conducting electrolyte on the catalytic activity towards ammonia synthesis, were investigated with the use of a Ni catalyst. It was found that proton-conducting oxide BZCY has promotion effects on the catalytic activity towards ammonia synthesis
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