Additionally, to reinforce the zeolite with nano-layers of zinc (Testbourne©, UK), raw ZSM-5 was plasma-sputtered with zinc longitudinally on half of the zeolite pellet surface using a coating machine based on the technology of scanning electron microscopy (FEI Quanta 200 Environmental, FEI Company©). The sputtering technique allows using an argon plasma stream under a vacuum to separate zinc metal atoms off a zinc disc target by applying a high voltage to initiate plasma gas ion exchange. The plasma sputter anchored the active metal (zinc) atoms onto the surface of the ZSM-5 zeolite pellets as an ultra-thin film. Technical difficulties in materialising this approach using the said machine and the substrate zinc disc resulted in having a very limited number of repeats for this addendum and hence the outcome of the zinc sputtering of zeolite is anecdotal. The zincsputtered zeolite treatments [ZnSZ-M] and [ZnSZ+M] were, therefore, excluded from the statistical analysis specified below.