Formation of Methanol over Copper-Zinc loaded Multi-walled Carbon Nanotubes using a Syngas feedstock

Abstract

Industrially, methanol synthesis is carried out over a Cu/Zn/Al2O3 catalyst using a feedstock consisting of CO/CO2/H2, otherwise known as syngas. Multiple publications have made use of multi-walled carbon nanotubes, otherwise known as MWCNTs as a catalyst support due to their high surface area. We attempted to produce a number of catalysts by means of incipient wetness impregnation using copper and zinc nitrates on oxidised MWCNTs. Some of these preparations underwent treatments to remove externally deposited metals, and leave only the inside deposited metal. Transmission electron microscopy showed that the selective deposition techniques were not successful, and by using a solution that will produce a 7.2 wt% Cu loading, similar results were achieved. Cu wt% loadings of 14.4+ produced large sized metal particle with large clusters found on the external nanotube surface. A signifcant discrepancy of 20% was observed between the intended and actual Cu wt% loading.Under methanol synthesis conditions the produced catalysts performed best at a 4 vol% CO2 feedstock concentration. We tested the catalysts for a total of 160 hours and found that catalysts which had lower copper content had shorter lifespans in comparison to the higher copper content counterparts. The catalyst prepared with an 18 wt% Cu loading (13 wt% EDX) was found to have a 25% CO+CO2 conversion into methanol which was the standout from the produced catalysts. 25% is also the upper limit for this particular reaction. Lastly, a number of new avenues of further possible investigation were identifed.