NiMg Based Catalyst for the Complete Oxidation of Methane in Natural Gas Vehicle Exhaust

Gianni  Caravaggio, Natural Resources Canada, CanmetENERGY

G. Caravaggio*, L. Nossova and R. Burich,

Natural Resources Canada, CanmetENERGY-Ottawa, 1 Haanel Drive,                Ottawa, Ontario K1A 1M1 Canada

*corresponding author: gianni.caravaggio@canada.ca

 

The use of natural gas (NG) as a road fuel is increasing due to its low cost, accessibility and environmental benefits. There are approximately 25 million NG vehicles in the world currently and NG use in transportation is expected to have a compound annual growth rate of 2% from 2019 to 2025[i]. The heavy-duty truck market alone is predicted to rise from $120 billion USD currently to $160 billion USD in 2025ⁱ. Lean burn NG engines are similar in performance to diesel engines and as such, they are especially suitable for heavy-duty vehicles. NG vehicles also have the advantage of lower GHG (up to 20%) than diesel or gasoline[ii]. However, these NG vehicles suffer from unburnt methane emissions (methane slip) that can significantly reduce the GHG benefit of the vehicle. Typically, Pd containing catalysts can be used to eliminate methane slip. However, they are prone to rapid deactivation due to sintering and are sensitive to water inhibition. Further, Pd is expensive.

The objective of this work was to develop a methane oxidation catalyst with activity similar to or better than Pd-based catalysts using less expensive metal oxides. For this purpose, Ni_0.9Mg_0.1O_x (molar ratio of Ni:Mg=9:1) mixed oxides catalysts were prepared using co-precipitation, ultrasonic spray pyrolysis and sol-gel methods and tested for methane oxidation activity. The catalysts were characterized using XRD, BET surface area technique and SEM/EDX. Preliminary methane oxidation evaluation was performed using temperature programmed oxidation with a mixture of 1%CH₄ and 10%O₂ without the presence of water. The Ni_0.9Mg_0.1O_x catalyst activity was compared to that of pure NiO. Ni_0.9Mg_0.1O_x prepared by co-precipitation exhibited the highest methane oxidation activity.

The best performing co-precipitated catalyst was further tested in the presence of water to determine the effect of water on methane oxidation activity. This catalyst was then aged at 500°C for 16 hrs and compared to a 1% Pd/Al₂O₃ reference catalyst aged under the same conditions. Under these conditions, the NiMg co-precipitated catalyst showed higher methane conversion and stability than a 1%Pd/Al₂O₃ reference catalyst.

[i] Global Market Insights, 2019, https://www.globenewswire.com/news-release/2019/04/01/1790370/0/en/Heavy-Duty-Truck-Market-value-to-hit-160bn-by-2025-Global-Market-Insights-Inc.html

[ii] Balasubramanian Viswanathan Energy Sources Fundamentals of Chemical Conversion Processes and Applications, 2017, Pages 59-79