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The surface morphology of Li-promoted MgO catalysts prepared using the sol-gel method (sg) and wet impregnation procedure (imp), respectively, has been studied by low-temperature infrared spectroscopy of adsorbed CO molecules. The results show that step sites, as unselective catalytic centers, are the major features existing on the surface of pure MgO, and those are active toward the oxidative conversion of propane. However, the concentration of these sites is drastically reduced by the incorporation of lithium ions in the MgO lattice. In fact, the incorporated Li (+) ions tend to move into the surface region and occupy sites associated with lower coordination number (e.g., step sites). Li/MgO-sg catalysts are characterized by a higher concentration of incorporation of lithium compared to Li/MgO-imp. In the case of oxidative dehydrogenation/cracking of propane, Li/MgO-sg catalysts show higher activity and selectivity to olefins compared to materials prepared using wet impregnation. Catalytic performance differs strongly regarding (i) the amount of olefins formed, and (ii) the ratio of C(3)H(6)/C(2)H(4). It is shown that high density of active sites is essential for further oxidative dehydrogenation of propyl radicals to propylene and suppression of cracking reactions pathway.

In this work, the oxidative conversion of propane was studied using a dielectric barrier discharge microreactor. This generates a cold microplasma at atmospheric pressure and ambient temperatures. Surprisingly, large amounts of products with molecular weight higher than propane, such as C 4 and C 4 +, were mainly observed due to C-C bond formation, in contrast to what is usually observed for this reaction when it is carried out under thermal activation, which leads to cracking products. A chemical kinetic model was developed to better understand the radical reaction network. Interestingly, the results suggest that (i) at lower level of propane conversion the model can nicely predict the experimental results and (ii) depending on the radical density the product selectivity can be tailored. In particular, at higher radical density, enhanced C-C bond formation was observed.

In this work, oxidative cracking of propane was studied in a microreactor containing a catalyst. A dielectric barrier discharge (DBD) allows one to generate a cold microplasma, which activates propane forming radicals, at room temperature and atmospheric pressure. Homogeneous and well crystalline thin layers of MgO and Li/MgO catalysts, 25 µm thicknesses, were deposited in the microchannel using sol-gel method and by micropipetting. Li/MgO catalyst showed higher propane conversion and olefins selectivity compared to MgO. The latter one suggests that (i) radicals formed by DBD in gas phase are differently terminated depending on the catalyst surface and (ii) the surface of Li/MgO catalyst present more selective sites than MgO, such as [Li + O -] centers and F-type defects that are generated and able to react at room temperature. Surprisingly large amounts of products with higher molecular weight than propane, that is, C 4 , C 4 + were also observed due to only C-C bond formation.