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Experimental observations and simulation results regarding a pure He atmospheric pressure plasma jet (APPJ) and He + N 2 APPJs interacting with a downstream dielectric substrate are presented in this paper. Experiments utilizing spatialtemporal imaging show that, in the case of the pure He APPJ, an annular plasmasubstrate interaction pattern is formed. With the introduction of N 2 , the plasma is more uniformly distributed on the substrate surface, appearing a solid interaction pattern. The experimental measurements indicate 0.5% N 2 mixture is the optimal condition to achieve the most intense discharge, while the plasma substrate contact area is slightly reduced by 6.1% in comparison to that of the pure He APPJ. A 2D selfconsistent fluid model is constructed to provide insights into the role of the addition of trace of N 2 on the discharge dynamics. The discharge morphologies predicated by the model is in principle consistent with the experimental observations. The simulation reveals that the conversion from the annular plasmasubstrate interaction pattern to the solid one is attributed to the synthetic effect of the addition of N 2 and the presentence of the substrate acting as the cathode to enhance the local electric field. In the solid interaction pattern, the Penning ionization makes a significant contribution to the surface discharge, especially in the afterglow region. The dominant positive ions (N + 2 and N + 4 ) and the reactive oxygen and nitrogen species including O and N gain remarkable increment in the flux intensity to the central surface, which merits great application potential.

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The production of alkyl levulinates from cellulose was successfully achieved by using a simple and efficient metal salt catalyst, Al2(SO4)3, offering a high yield up to 70.6% under microwave conditions within a short reaction time of 40 minutes.