Solid Base Assisted n-Pentanol Coupling over VIII Group Metals: Elucidation of the Guerbet Reaction Mechanism by DRIFTS

Abstract

Liquid phase catalytic coupling of n-pentanol over VIII group metals (Pt, Pd, Ir, Ru, Rh) on a range of supports (C, Al2O3, TiO2, CeO2, ZrO2) doped with different solid bases was done varying the reaction temperature and gas atmosphere. It was shown that n-pentanol coupling in the selected reaction conditions (180 °C, 10 bar of N2) mainly resulted in the formation of the target product 2-propyl-1-heptanol (Guerbet alcohol), whereas pentanal, 2-propyl-2-heptenal, 2-propyl-1-heptanal, and 2-propyl-1-heptenol were observed in minor quantities. Temperature increase accelerates the reaction and improves selectivity to 2-propyl-1-heptanol. Acid–base properties of the supports also influenced conversion and selectivity correlating with the support base strength TiO2 (860 kJ/mol) < ZrO2 (900 kJ/mol) < C (850–910 kJ/mol) < Al2O3 (935 kJ/mol). For carbon supported catalysts conversion increases in the raw Ir < Ru < Pt < Pd. Analysis of the reaction mechanism for NaOH/Pt/Al2O3 and the relative contributions of various catalytically active phases was done by in situ Fourier transform infrared spectroscopy.

Chemoselective heterogeneous iridium catalyzed hydrogenation of cinnamalaniline

“…The small differences in selectivity towards unsaturated amine 2 between alumina and zirconia supported catalysts can be correlated with the metal oxide base strength, which in terms of proton affinity was estimated to be similar for ZrO 2 (900 kJ/mol) and Al 2 O 3 (935 kJ/mol). 23 For iridium supported on silica, alumina and zirconia, the conversion of cinnamalaniline increases in the series: SiO 2 <<< ZrO 2 ~ Al 2 O 3 , for the last two supports the yields of the unsaturated amine 2 and undetectable side products were also comparable.…”

The Role of Copper in the Upgrading of Bioalcohols

“…Ru and Ag produced acetaldehyde with ≈50 % selectivity, whereas Rh and Pd formed diethylether as the main product . A very high selectivity to Guerbet alcohol (89.9 %) was observed by reacting n ‐pentanol in the presence of Pt/Al 2 O 3 and NaOH (Table , entry 13) during the investigation of the reactivity of n ‐pentanol over precious metal catalysts (Pt, Pd, Ir, Ru, Rh) supported on different solids (C, Al 2 O 3 , TiO 2 , ZrO 2 , CeO 2 ). The strength of the support basic sites was found to correlate with activity and selectivity following the order TiO 2 <ZrO 2 <Al 2 O 3 .…”

“…Ru and Ag produced acetaldehyde with % 50 %s electivity,w hereas Rh and Pd formed diethylether as the main product. [27] Av ery high selectivity to Guerbet alcohol (89.9 %) was observed by reacting n-pentanol in the presence of Pt/Al 2 O 3 and NaOH (Table 1, entry 13) [28] during the investigation of the reactivity of n-pentanol over precious metal catalysts (Pt, Pd, Ir,R u, Rh) supported on different solids (C, Al 2 O 3 ,T iO 2 ,Z rO 2 ,C eO 2 ). The strength of the support basic sites was found to correlate with activity and selectivity following the order TiO 2 < ZrO 2 < Al 2 O 3 .A ne xtensive investigation on the activity of Cu, Ni and Co supported on alumina conducted at 240 8Ca nd pressures up to 100 bar,s howed that 1-butanol was selectively formed (selectivity = 60-65 %a t2 5% conver-sion )o ver 19 %N i/Al 2 O 3 whereas 16 %C o/Al 2 O 3 gave ethyl acetate with up to 85 %s electivity.…”

Electronic and steric factors for enhanced selective synthesis of 2-ethyl-1-hexanol in the Ir-complex-catalyzed Guerbet reaction of 1-butanol

“…For example, the Guerbet reaction of ethanol, a fermentation product of sugar-containing crops, has been studied to produce 1-butanol as an "advanced biofuel." Heterogeneously and homogeneously catalyzed Guerbet reactions of ethanol to 1-butanol have been reported [7][8][9][10][11][12][13][14][15][16][17][18][19][20]. 1-Butanol is also a potential fermentation product obtained via the acetone-butanol-ethanol fermentation process [21][22][23][24].…”

“…Compared with the conventional three-step process in the production of 2-EH from fossil resources, the synthesis of 2-EH through the Guerbet reaction offers technical and potentially economic advantages, as it is a one-step process that eliminates the need for operations under pressurized CO and H2. Heterogeneous catalysts, such as Ir on N-doped carbon and Pd on metal oxides, have been applied for the Guerbet reaction of 1-butanol to 2-EH under a high temperature (> 170 °C) with byproducts including olefins, ethers, and higher alcohols [27][28][29]. Homogeneous catalysts, such as Ir complexes, have been reported to exhibit good catalytic dehydrogenation/hydrogenation functions involved in the Guerbet reaction of 1-butanol.…”