# Performance of Granulated Ti-Dopped Manganese Oxide Oxygen Carriers in Chemical Looping Processes
## 5 Conclusions  
Manganese-titanium mixed oxides with different Ti/(Mn+Ti) molar ratios in the 0-0.49 range (corresponding to 0-50 wt.% TiO\({}_{2}\)) were prepared by granulation in a high shear mechanical mixing granulator and calcined in air under the same conditions as those used with particles of identical composition but prepared by pelletization. The granulation method can improve the scalability of the production of these oxygen carrier particles as well as influence their reactivity. Once calcined, granulated particles presented similar composition obtained by XRD: mostly Mn\({}_{2}\)O\({}_{3}\), with low amounts of Mn\({}_{3}\)O\({}_{4}\) and an important part of TiO\({}_{2}\) in the form of pyrophanite (MnTiO\({}_{3}\)). However, the crushing strength of granulated particles was lower, although higher than 1 N. Both particles prepared by granulation and pelletization showed a maximum in the oxygen transport capacity for oxygen release in the Ti/(Mn+Ti) range of 0.15-0.2 at the two temperatures considered, i.e., 850 and 940 \({}^{\circ}\)C. Thus, the mixed oxide with 20 wt.% TiO\({}_{2}\) (MnTi_20) was tested further. MnTi_20 showed high reactivity to H\({}_{2}\) and maintained it for almost 200 redox cycles in TGA. However, after this long testing, mechanical properties were worsened compared to the calcined material: mechanical strength decreased to values lower than 1 N, and porosity significantly increased, making particles more fragile for breakage. Regarding the performance of MnTi_20 under fluidized conditions, the material also showed the ability to release oxygen and regenerate at temperatures higher than 850 \({}^{\circ}\)C, although the oxidation rate was low at 950 \({}^{\circ}\)C. Reactivity with H\({}_{2}\) and CO at 950 \({}^{\circ}\)C was also high, comparable to that previously found with manganese-based minerals, although not as high as that reported for an impregnated Mn-based oxygen carrier. Nevertheless, neither manganese minerals nor the impregnated oxygen carrier showed CLOU properties. No agglomeration or fluidization problems were encountered, and the lifetime of the material after 60 h of continuous fluidization was estimated as roughly 2500 h. This value is one of the highest found in literature for manganese-based oxygen carriers. This behavior in the batch fluidized bed makes this material a promising oxygen carrier to be considered in different CL processes. Its improved CLOU properties enable it to compete against manganese-based minerals, and its reactivity is of the same order and similar to that of other synthetic materials, such as manganese-iron mixed oxides. Conceptualization, T.M. and A.A.; methodology, T.M., A.F. and A.A.; validation, T.M. and A.F. ; formal analysis, T.M., A.F. and M.T.I. ; investigation, T.M., A.F. and M.T.I. ; resources, T.M. and A.A.; data curation, T.M. and M.T.I. ; writing--original draft preparation, T.M. ; writing--review and editing, T.M. and I.A.-R.; visualization, T.M. and I.A.-R.; supervision, T.M. and I.A.-R.; project administration, T.M. and A.A.; funding acquisition, T.M. and A.A. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the PDC2021-121190-I00/ AEI/10.13039/501100011033 financed by MCIN/ AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR. The authors also thank the funding received from Gobierno de Aragon--Dpto. de Ciencia, Universidad y Sociedad del Conocimiento--Project LMP166_21. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Data will be available on request. **Acknowledgments:** [PERSON] acknowledges for \"Ramon y Cajal\" Program (Grant RYC2022-035841-I funded by MCIU/AEI/10.13039/501100011033 and FSE+). **Conflicts of Interest:** The authors declare no conflicts of interest.