Effects of Organic Modifiers on a Palladium Catalyst in the Competitive Hydrogenation of 1‐Octene Versus Octanal: An Evaluation of Solid Catalysts with an Ionic Liquid Layer

Abstract

The competitive hydrogenation between 1‐octene and octanal has been investigated with a ≈5 % palladium on alumina catalyst prepared in situ with the following organic modifiers: pyridine, 1‐methylimidazole, 1,3‐dimethylimidazole methylsulfate, 1,3‐dimethylimidazole bis(trifluoromethylsulfonyl)imide and methyltri‐sec‐butylphosphonium methylsulfate. The results of these investigations indicate that the ionic liquid modifiers have significant and specific effects on catalytic performance, for example, certain systems can completely suppress octanal conversion. In addition, analytical techniques reveal that the matrix and quantity of organic species on the used catalysts are different if different ionic liquids are used as modifiers. Surface studies also reveal that the modifiers have a noticeable effect on the crystallite size and chemisorption properties of the catalysts.

Activity and Selectivity of a Nickel SCILL Catalyst in the Competitive Hydrogenation between 1-Octene and 1-Octyne

“…Common characterization data for these catalysts have been described previously. 11,12 Electron microscopy work was conducted on a All other catalyst characterization techniques have been described previously, as has the hydrogenation experimental setup in a concurrent down flow trickle bed reactor. 11,12,32 In this study, the hydrogenation reaction was carried out by using a hydrogen pressure of 50 bar.…”

“…11,12 Electron microscopy work was conducted on a All other catalyst characterization techniques have been described previously, as has the hydrogenation experimental setup in a concurrent down flow trickle bed reactor. 11,12,32 In this study, the hydrogenation reaction was carried out by using a hydrogen pressure of 50 bar. It is well-established that gas solubility correlates with the partial pressure of the gas.…”

“…This may be the result of the defects observed in the crystallites from the HRTEM analysis, as defects are associated with increased reactivity. 11,12,32 This could explain why the catalysts prepared by method B are inactive in the hydrogenation reactions, as the catalysts prepared by method B are rapidly oxidized after exposure to the atmosphere. The time required for coating the catalyst with ionic liquid or charging the reactor with this catalyst might therefore be longer than the time required for the catalyst to reach a level of oxidation that cannot be reduced under the conditions the catalyst is exposed to before the commencement of a reaction.…”

“…7−10 Recently, we have reported potential catalytic evidence for site-specific interactions (by the ionic liquid) affecting selectivities in the competitive hydrogenation of 1-octyne and 1,7-octadiene versus 1-octene, in which surface diffusion effects may also occur. 11,12 Alkyne and diene hydrogenation studies have been the focus of much attention in the literature but have traditionally been restricted to short-chain molecules such as C 2 and C 4 compounds. 7,13−15 However, relating the behavior of these short-chain compounds to longer-chain versions is fraught with difficulties.…”

“…The original thought behind this modification was to increase selectivity based on solubility differences between reactants in the ionic liquid . However, literature reports suggest that other processes may be occurring which may influence the selectivity and activity of the reaction. − For example, in the hydrogenation of molecules containing multiple reducible groups, changes in the selectivity of hydrogenation between these groups have been demonstrated. − Infrared studies have also shown that the cation of an ionic liquid can occupy and potentially block specific sites on a catalyst surface, which vary depending on the metal used and may be responsible for these changes in selectivity. − Recently, we have reported potential catalytic evidence for site-specific interactions (by the ionic liquid) affecting selectivities in the competitive hydrogenation of 1-octyne and 1,7-octadiene versus 1-octene, in which surface diffusion effects may also occur. , …”