This presentation will cover the synthesis and characterization of a pool of different supported metal oxide catalysts, highlighting the role of various promoters on the dispersion of metal oxides on SiO2 and the synergetic effect of mixed transition metal oxides at sub-monolayer and monolayer coverage. Experimentally achieved vanadia dispersion on SiO2 is only ~3 V/nm2, far lower than the vanadia dispersion on all other oxide supports which show ~9 V/nm2.1 We found that the typical, close to the theoretical 9 V/nm2 monolayer coverage can also be achieved upon addition of promoters to pure amorphous silica.2 Carefully characterization by a variety of techniques such as ICP-OES, BET, in situ Raman, UV spectroscopy and 51V-NMR evidences a new record for vanadia dispersion on SiO2. Moreover, we also have used the oxidative dehydrogenation of propane as a complementary characterization technique to confirm the uniquely presence of two-dimensional VOx species. Indeed, propylene selectivity is drastically reduced by the formation of V2O5 nanoparticles above monolayer coverage.3 Our new approach also allows the dispersion of Nb and Ta at loadings higher than the current state-of-the-art.4 Interestingly, by using promoted SiO2, the propane consumption rate is not affected whereas the propylene combustion rate as a function of propane conversion is improved. Moreover, aimed to enhance the productivity toward olefins and following a previously reported study,5 several different transition metal oxides were dispersed on promoted SiO2. We will discuss preliminary data regarding our current work, aimed at i) understanding the role of promoters on the dispersion of different metal oxide catalysts on SiO2, ii) maximizing the positive synergetic effect between promoter and vanadia in the propylene combustion rate and iii) combine different metal oxides at sub-monolayer and monolayer coverage in order to tune both the (Brønsted and Lewis) acidic and redox properties for different catalytic applications.
1. Carrero, C. A.; Schlögl, R.; Wachs, I. E.; Schomäcker, R. ACS Catal., 2014, 4, 3357-3380
2. Grant, J.; Carrero, C. A.; Hermans, I. Patent issued February 2015, United States 62/112, 689
3. Carrero, C. A.; Keturakis, C. J.; Orrego, A.; Schomäcker, R.; Wachs, I. E. Dalton Trans., 2013, 42, 12644-12653
4. Tian, H.; Roberts; Wachs, I. E. J.Phys.Chem. C 2010,114,14110–14120
5. Carrero, C. A.; Kauer, M.; Dinse, A.; Wolfram, T.; Hamilton, N.; Trunschke, A.; Schlögl, R.; Schomäcker, R. Catal. Sci. Technol., 2014, 4, 786-794