The Effect of Lanthanum on The Performance of Pt-Sn/Al2O3 Reforming Catalysts
Advancing the chemical engineering fundamentals
Catalysis (T2-13P)
Keywords: Catalytic Reforming, PtSn/Al2O3-La2O3, catalysts deactivation, acidity, TPD of ammonia, NMR Al27.
The Catalytic Reforming (CR) is still one of the basic petroleum refining processes and the bimetallic bifuntional catalysts used have been widely investigated. However, today the catalysts deactivation by coke formation and benzene production continue being the main challenges in this process.
In the present work the effect of lanthanum on the catalytic behavior of the bifuntional PtSn/Al2O3 reforming catalyst has been investigated. Lanthanum was introduced during the synthesis of the Al2O3 by the sol-gel method to form an Al2O3-La2O3 mixed oxide. The lanthanum content employed was 5 and 15 wt% (Al2O3-La2O3-5 and Al2O3-La2O3-15, respectively). The n-heptane reforming at 500°C was used as a test reaction and according to our results lanthanum seems to be one of the most promising additives because it provides a total benzene inhibition and long lifetime (17% deactivation at 50 min. reaction time). Changes in the catalytic behavior due to differences of the acidity and the support-metal interaction were observed.
The surface area is increased with lanthanum content, reaching its maximum at 15% of La2O3 content. Acid site density is diminished, while the base site density is increased with the introduction of lanthanum. Furthermore, the higher base site density (at 15 wt% of La2O3) correlates very well with the inhibition of benzene and resistance to deactivation of the PtSn/Al2O3-La2O3-15. By FTIR-pyridine thermo-desorption it was determined that alumina has mainly Lewis acid sites although a small signal attributed to Brönsted acid sites was present up to 200°C. For mixed oxide solids (Al2O3-La2O3), as the La content was increased, the strength of the Lewis acid sites decreased and the strength of the Brönsted acid sites increased. X-ray diffraction results showed that at 520°C the alumina-lantana mixed oxides were amorphous. In contrast, Electron Diffraction Patterns suggested that there are crystalline micro-domains. The existence of one phase of lanthanum aluminate in the mixed oxides was determined, LaAl11O18 (33-699 JCPDS card) was detected and it could be responsible for the changes in the acid-base properties of the support.
On the other hand, lanthanum also modifies the coordination spheres of aluminum due to its introduction to the Al2O3 framework. A decrease of aluminum in octahedral environment AlVI (3.5 ppm) as well as an increase of the pentahedrally coordinated AlV (32 ppm) as a function of the lanthanum content was observed by MAS NMR.
Presented Wednesday 19, 13:30 to 15:00, in session Catalysis (T2-13P).
