Role of rhenium in Pt‐Re‐Al₂O₃ reforming catalysis—An integrated study

Abstract

The inclusion of Re in Pt-Re-AlzO3 reforming catalysts to improve the lifetime is known, but how rhenium functions and how it is disposed in the catalyst remain unclear. These fundamental questions have been attempted in this study by the use of proton-induced X-ray emission and Rutherford backscattering spectrometry (together with electron microscopy and chemisorption studies) to characterize a commercial like catalyst for dehydrogenation of methylcyclohexane. Catalysis is one of the most intensely pursued subjects in chemical engineering and related disciplines, primarily because of its economic importance. The development of modern surface science has made possible studies of the catalyst surface at the molecular level, leading to a better understanding of its role in determining catalytic activity. In situ measurements by infrared spectroscopy (Eischens and Pliskin, 1958;Blyholder, 1968; Force and Bell, 1975a,b), Mossbauer spectroscopy (Dumesic and Topsoe, 1977), electron spin resonance (Lunsford, 1972) and X-ray diffraction (Srivastava et al., 1982) have enabled chemical engineers to broaden their thinking beyond the semiempirical reaction parameters, and relate them to structural aspects of the catalyst, thus leading to a more comprehensive and integrated modeling of chemical reactors.In spite of the applications of advanced instrumental techniques in catalysis, there have been great difficulties inherent in studying the structure and composition of surface atoms in dispersed high area systems such as Pt-Re-AlzO3, the industrial reforming catalyst. Platinum-rhenium-alumina catalysts contain an amount of rhenium comparable to the amount of platinum present (about 0.3 wt. % of each). The addition of rhenium provides greater stability; however, the reasons for the promotional effect of rhenium are unclear, despite some 25 reported studies. It is important to understand how rhenium functions if alternate and better catalyst systems are to be developed. The impact of the research in this bimetallic catalyst area is likely to increase over the next few years. For example, the MTH (methylcyclohexane-toluene-hydrogen) system using methylcyclohexane as a hydrogen carrier, which requires the catalytic (Pt-Re-AlzOs) production of hydrogen from an on-board reactor, is commercially exploited for automotive application (Cresswell et al., 1984).The application of proton-induced X-ray emission analysis (PIXE) and Rutherford backscattering spectrometry (RBS) can provide a significant insight into the near surface elemental composition. Both these techniques were designed originally for research in nuclear physics, and tended to be temperamental and complicated. Most accelerators are now designed for material analysis; however, the full potential of PIXE and RBS techniques in catalyst research has not yet been exploited.In this investigation, results are postulated using the techniques of proton-induced X-ray emission and Rutherford backscattering spectrometry with complementary data from electron microscopy and chemisorptio...

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

“…The introduction of the second metal (i.e., Ir and Re) to Pt can remarkably improve the selectivity of aromatics and prolong the catalyst's lifetime. 4,5 In another example, bimetallic AuPd catalysts are used for the production of vinyl acetate monomer by the reaction between acetic acid and ethylene in the presence of oxygen. 6 Pd is the main functional component, while adding Au can improve Pd particles' stability by protecting them from sintering.…”

“…For instance, the industrial naphtha reforming catalysts based on Pt-based bimetallic particles (e.g., PtIr and PtRe) supported on Al 2 O 3 have played a crucial role in the conversion of alkanes into aromatics. The introduction of the second metal (i.e., Ir and Re) to Pt can remarkably improve the selectivity of aromatics and prolong the catalyst’s lifetime. , In another example, bimetallic AuPd catalysts are used for the production of vinyl acetate monomer by the reaction between acetic acid and ethylene in the presence of oxygen . Pd is the main functional component, while adding Au can improve Pd particles’ stability by protecting them from sintering.…”

Dehydrogenation mechanisms of methyl-cyclohexane on γ-Al2O3 supported Pt13: Impact of cluster ductility

“…[22,23,[30][31][32][33] A second metallic element such as rhenium [34][35][36][37][38] or tin [31,32,[39][40][41][42] is often added to improve the selectivity to aromatics and reduce deactivation of catalysts by coke formation. [34,39,40,43,44] The superior activity of platinum for C-H bond scission and low activity for C-C bond cleavage also made the alumina supported platinum catalyst as a popular choice for the non-oxidative dehydrogenation of light olefins. [15] In the case of reforming, alumina is the most suitable support enabling the good dispersion of Pt clusters and catalyzing cyclisation and isomerization reactions, through the possible addition of a chlorine dopant modulating the acidity of the support.…”

An Efficient Strategy in Microemulsion Systems to Prepare Mono‐ and Bimetallic Platinum‐Rhenium Reforming Nanocatalyst with Remarkable Catalytic Performance

“…Combination of the two types of active sites may be promote the catalyst action and prevent undesirable reaction such as coke formation on the active site. The metal function is often used mixture with other promoters to forms a bimetallic catalyst such as Pt−Re, which is more selective and stable than pure metal . Obviously dispersion and degree of interaction between metal and support have a great influence on activity of reforming catalyst, which is dependent to preparation method .…”