Synthesis And Screening Na-Mn-W/SiO₂ Catalysts For Oxidative Coupling Of Methane Reaction Based On Ink-jet Printing Technology

C2 hydrocarbon is the foundation of modern industry, which mainly depends on petroleum cracking. Industrialization of oxidative coupling of methane (OCM) reaction to obtain C2 hydrocarbons is of great significance, which will replace the traditional petroleum cracking routine. Among the catalysts have been developed, Na-Mn-W/SiO2 is becoming the most promising system which has high CH4 conversion, high C2 selectivity and good stability.C2Fast ink-jet printing synthesis system has many advantages, such as huge (one formulation will contain more than 8 kinds of elements), fast (1,000,000 materials/h), economization, exactness (concentration control will reach 1/1000 molar), which contribute to control materials' composition accurately. With the idea of combinatorial chemistry and divided-into-groups screening strategy, we synthesized and screened different formulations of Na-Mn-W/SiO2 system catalysts in order to optimize their compositions.Developed Na, Mn, W printing inks, made standard curves of these elements to ensure printing precision and construct Na-Mn-W/SiO2 catalyst system library, using C2Fast ink-jet printing synthesis system.643 group catalysts have been tested whose catalytic condition is that GHSV is 20000h-1, CH4:O2:N2 is 3:1:2.6, reaction temperature is 800?, using 2%Na2WO4-2%Mn/SiO2 and 5%Na2WO4-2%Mn/SiO2 samples as reference provided by SHELL Company.This paper focused on W, Mn, Na color space [0,100], [0,100], [0,100] for first round screening, which obtained G4 space to be the best catalytic performance group (corresponding to the color space [0,50], [50,100], [50,100]), whose yield is 17.40%. When narrowed G4 space for second round screening, better catalyst groups were not obtained.What's more, randomly mixed different granular catalysts for experiments, such as whole-space mixing, half-space mixing and diagonal-space mixing to confirm that different catalysts'synergism is helpful to enhance catalytic performance.Based on the experimental results of mixing effect, further expanded the spatial screening on the basis of first round space. When mass concentration of W, Mn, Na is 6.11?12.22 wt%,6.57?13.14 wt%,1.27?2.54 wt%(corresponding to the color space [100,200], [100,200], [100,200]), catalyst's C2 yield reached 20.53%, which is higher than 5%Na2WO4-2%Mn/SiO2 provided by SHELL Company (C2 yield is 18.86%). The selected formulation has not been studied before.At the same time, XRD, ICP, XPS were used. In the XRD spectrum of Na-Mn-W/SiO2 system catalysts, activity phases are Na2WO4, Mn2O3 and ?-cristobalite, which are higher and more stable in Naioo-2ooMnioo-2ooWioo-200 (mass concentration for W,Mn,Na is 6.11?12.22 wt%,6.57?13.14 wt%,1.27?2.54 wt%). ICP and XPS results show that mass concentration of W, Mn, Na in Naioo-200Mnioo-2ooWioo-200 are higher than SHELL's samples. Testing result of Na for XPS (8.29 wt%) was higher than that of ICP testing (0.508 wt%). W for XPS (23.04 wt%) was also higher than ICP testing (2.17 wt%). However, Mn for XPS testing (4.57 wt%) was almost the same with ICP testing (4.11 wt%). We speculated that in Na-Mn-W/SiO2 catalyst system, Mn element was uniformly distributed, Na and W elements were mainly enriched on the surface of the support.