Selective catalytic and kinetic studies on oxydehydrogenation of ethane with CO2 over lanthanide metal catalysts

Abstract

Single metal catalysts with different active components (La, Sm, Ce) and La loadings (5%, 10%, 15%) were prepared. Oxydehydrogenation of C 2 H 6 with CO 2 over the above catalysts was studied by catalyst activity experiments and characterization tests. The results indicate that the homogeneous reaction of CO 2 /C 2 H 6 is the coupling of ethane pyrolysis and hydrogenolysis. Dehydrogenation has better selectivity than reforming on La/Sm/Ce-based catalysts; Sm exhibits the best catalytic activity due to carbon deposition resistance and many oxygen vacancies. C 2 H 6 conversion on 10% Sm/SiO 2 is 42.75% at 700°C, but C 2 H 4 selectivity is lowest. Because of the existence of Ce 4+ , Ce has the best C 2 H 4 selectivity; it has potential to modify the catalyst, but its catalytic activity is lowest. La shows the best catalytic performance. The activation energy on 10% La/SiO 2 is 83.99 kJ/mol, C 2 H 4 selectivity is 96.84% at 700°C, and its optimum loading is between 10% and 15%.

Ethane Oxidative Dehydrogenation over Pt-Rare Earth Intermetallic Compounds with CO2 as Soft Oxidant

“…As the CO 2 /ethane ratio increased, more CO 2 molecules might occupy the surface of Pt 5 La 1 intermetallic compounds, which led to a decrease in accessible adsorption sites for ethane and consequent conversion of ethane. Furthermore, a progressive decrease in ethane conversion for CO 2 /C 2 H 6 = 2 could be attributed to the poisoning effect of CO 2 , which was described elsewhere. , The addition of REE (particularly La) is known to increase the basicity of a catalyst. ,, Therefore, a possible reason for the decrease in ethane conversion with the increase in CO 2 in the feed flow in comparison to ethane was that CO 2 was acidic and was more attracted to basic sites (stems from REEs), which is discussed somewhere else. , Thus, excess CO 2 exhibited a negative behavior by superseding the adsorbed ethane.…”

“…TGA (Figure S4) of the catalysts confirmed coke deposition as the main cause of catalyst deactivation, which increases in the following order: 1Pt-1La@ZNS (1.32 wt %), 1Pt-1Y@ZNS (2.2 wt %), 1Pt@ZNS (2.4 wt %), and 1Pt-1Sc@ZNS (3.3 wt %). It is thus important that CO 2 activation is crucial for preventing coke from depositing on catalyst surfaces, which can help to keep the metal active sites open to reactants. , More importantly, compared to Y and Sc, La exhibited better CO 2 activation (Figure c), leading to the oxidative dehydrogenation of ethane and presenting the potential to minimize coke accumulation on the catalyst surface. This might be attributed to the fact that YO x and ScO x could not effectively activate CO 2 .…”

“…Wang et al studied the effect of different La loading values on SiO 2 . They observed that with increasing La content, the catalyst activity increased but the ethylene selectivity decreased due to the formation of by-products . Thus, the LaO x content should be properly controlled to balance the reverse Boudouard and dry-reforming reactions to maximize the ethylene selectivity and catalyst stability.…”

“…They observed that with increasing La content, the catalyst activity increased but the ethylene selectivity decreased due to the formation of by-products. 34 Thus, the LaO x content should be properly controlled to balance the reverse Boudouard and dry-reforming reactions to maximize the ethylene selectivity and catalyst stability. Although the catalytic activity for CO 2 increased with LaO x species, no effective increase in activity occurred after a certain level (∼2 wt % herein).…”

“…It is thus important that CO 2 activation is crucial for preventing coke from depositing on catalyst surfaces, which can help to keep the metal active sites open to reactants. 14,34 More importantly, compared to Y and Sc, La exhibited better CO 2 activation (Figure 3c), leading to the oxidative dehydrogenation of ethane and presenting the potential to minimize coke accumulation on the catalyst surface. This might be attributed to the fact that YO x and ScO x could not effectively activate CO 2 .…”