# Performance of Granulated Ti-Dopped Manganese Oxide Oxygen Carriers in Chemical Looping Processes
## 3 Results  
### Granulated Particles: Comparison with Results from Particles Produced by Pelletization  
In the first study from the authors on the TiO\({}_{2}\) doping of manganese oxides [25], different Mn-Ti mixtures with Ti/(Mn+Ti) molar ratios between 0 and 0.49 were produced by pelletization. Mixtures of the corresponding powders of Mn\({}_{3}\)O\({}_{4}\) and TiO\({}_{2}\) were mixed in a ball and then pelletized by pressure in a hydraulic press. Then they were crushed and sieved to 100-300 \(\upmu\)m. Previous studies in literature demonstrated the influence of the particle size of original particles and the preparation method on the redox behavior of manganese oxides [28]. Thus, the objective of the present work was to produce Mn-Ti oxides by granulation following the same Ti/(Mn+Ti) molar ratios previously considered and compare their performance with that observed with particles prepared from pellets. The interest in producing particles by granulation lies in the fact that it is an easily scalable method for considering the commercial production of oxygen carriers. In this regard, a recent study also proposed the granulation method as a preparation procedure to up-scale a newly developed Si-doped manganese oxide [29]. In the present work, granulation parameters were optimized to obtain particles also within the 100-300 \(\upmu\)m range. Once produced, particles were calcined in air at 1030 \({}^{\circ}\)C during 2 h. Crushing strength tests and XRD analyses were done on the calcined granulated particles and compared to the previous values obtained with pellets. Table 1 and Figure 4 show a comparison of the properties and XRD phases of selected calcined samples regarding pellet-produced and granulated particles. Crushing strength values between 1.5 and 2.6 N were obtained for the granulated particles, while higher values were reached when the particles were produced from pellets. The results were obtained for the 100-300 \(\upmu\)m range. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Mn3O4** & **TiO2** & **Ti/(Ti + Mn) a** & **Crushing Strength** & \multicolumn{3}{c}{**XRD Main Phases (wt.\%)**} \\ \cline{5-8}  & **(wt.\%)** & **(wt.\%)** & **Ti/(Ti + Mn) a** & **(N)** & **Mn2O3 + Mn3O4** & **MnTiO3** & **TiO2** \\ \hline \multicolumn{8}{l}{**Pelletized samples**} \\ \hline MnTi1\_15 & 85 & 15 & 0.14 & 4.6 & 79.7 & 19.4 & 0.9 \\ \hline MnTi20 & 80 & 20 & 0.19 & 3.7 & 75.7 & 23.6 & 0.7 \\ \hline \multicolumn{8}{l}{**Granulated samples**} \\ \hline MnTi15 & 85 & 15 & 0.14 & 1.6 & 95.3 & 2.5 & 2.2 \\ \hline MnTi20 & 80 & 20 & 0.19 & 2.6 & 87.9 & 3.8 & 8.3 \\ \hline \hline \end{tabular}  
* \({}^{\mathrm{a}}\)Molar ratio.  
\end{table} 
Table 1: Main properties of Mn-Ti samples after calcination in air at 1030 \({}^{\circ}\)C for 2 h.  
Figure 4: XRD solid phases of (**A**) MnTi15 and (**B**) MnTi20 for calcined granulated particles and particles reduced in nitrogen at 850 \({}^{\circ}\)C and 940 \({}^{\circ}\)C.  
lets (3.3-5.5 N). XRD quantitative analyses of the granulated particles showed similar composition to that of pellet-produced particles. In both cases, the samples were mostly crystalline. The major phase observed was Mn\({}_{2}\)O\({}_{3}\), although some Mn\({}_{3}\)O\({}_{4}\) was detected in some cases, probably produced during the cooling-down of the sample in the muffle after calcination. Free TiO\({}_{2}\) was detected. In the case of pellets, the amount of free TiO\({}_{2}\) was not significant. Most of it was combined with Mn\({}_{2}\)O\({}_{3}\) to form pyrophosphate (MnTiO\({}_{3}\)). In the granulated particles, more free TiO\({}_{2}\) was observed, and the formation of pyrophosphate was more limited than in the case of the particles from pellets. This could probably be due to the cooling conditions in the muffle for the granulated particles, which may have favored the decomposition of MnTiO\({}_{3}\) to Mn\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) compared to the case of the pellet-produced particles.