Low temperature activation of Pt/Ni supported MCM-41 catalysts for hydrogenation of benzene

A series of Pt/Ni supported MCM-41 catalysts prepared via classical methods have been investigated. The promotional effect of low activation temperature is shown in comparison to higher temperatures. Surface properties of the catalysts activated at low temperatures were studied using H2-temperature programmed reduction (H2-TPR), H2-chemisorption and H2-temperature programmed desorption (H2-TPD) methods while the morphology and size distribution of the particles were obtained using transmission electron microscopy (TEM) analysis. Surface studies showed the promoting effect of Pt on the reduction of Ni species on the support. Total reduction only occurred for the Pt100 and Pt90Ni10 catalysts. Interestingly, it was found that the active phase of the monometallic catalysts were composed of spherical metal particles in the nanosize range, while the bimetallic catalysts showed a combination of spherical and large cubic particles. Tests on the gas phase hydrogenation of benzene show that Pt50Ni50 and Pt90Ni10 exhibit high activity when compared to Pt100, though both these catalysts contain lower atomic percentages of Pt. This can be attributed to the anchoring effect of non-reduced Ni2+ ions that result in well dispersed Pt particles. Kinetic studies were conducted to understand the surface chemical process of the bimetallic catalysts.

Pt/Ni–MCM-41 catalysts were prepared via co-impregnation using classical methods. Catalysts were activated at low temperatures. Pt50Ni50 and Pt90Ni10 catalysts exhibit high reactivity, due to the anchoring effect of Ni2+ ions.Figure optionsDownload high-quality image (83 K)Download as PowerPoint slideResearch highlights▶ Catalysts containing Pt and Ni as the active phases can be prepared via classical methods and still show optimum activity at low temperatures. The activation temperature employed in this work is only at 473 K for duration of 15 min. This is unusual for Ni based catalysts. A variety of characterization techniques were used to understand this phenomenon. Findings reveal two possible explanations for the enhanced catalytic activity and optimum activity at low activation temperatures: (i) alloying of the Pt/Ni metal phases or/and; (ii) anchoring of the Pt particles to Ni2+ ions attached to the support. ▶ Alloying of Pt and Ni is a common occurrence which can contribute to the enhanced reactivity. However, anchoring of the Pt particles to Ni ions is also an important aspect.