Armin Liebens

Silica-immobilized Aquivion PFSA superacid: application to heterogeneous direct etherification of glycerol with n-butanol

We report the effective heterogenization of polymeric perfluorosulfonic acid (PFSA) Aquivion® resin in a silica network for the direct etherification of glycerol with aliphatic n-butanol. The Aquivion-silica composites, prepared by a template-free sol–gel method, presented a large specific surface area, affording highly accessible acid sulfonic groups. The textural and bulk/surface properties of the hybrid composites were characterized in-depth using TGA, acid–base titration, N2 adsorption–desorption, XRD, TEM, FTIR, Raman, CP-MAS NMR and XPS. The Aquivion-silica composites exhibited a high catalytic activity (91% n-butanol conversion) and selectivity (45% butyl glyceryl monoether yield) while they lowered the formation of by-product (6% dibutyl ether yield) as compared to benchmark homogeneous and heterogeneous acid catalysts. The catalyst was reusable and maintained a stable performance after six consecutive cycles.

Direct dehydration of 1,3-butanediol into butadiene over aluminosilicate catalysts

The catalytic dehydration of 1,3-butanediol into butadiene was investigated over various aluminosilicates with different SiO2/Al2O3 ratios and pore architectures. A correlation between the catalytic performance and the total number of acid sites and acid strength was established, with a better performance for lower acid site densities as inferred from combined NH3-TPD, pyridine adsorption and 27Al-NMR MAS spectroscopy. The presence of native Bronsted acid sites of medium strength was correlated to the formation of butadiene. A maximum butadiene yield of 60% was achieved at 300 °C over H-ZSM-5 with a SiO2/Al2O3 ratio of 260 with the simultaneous formation of propylene at a BD/propylene selectivity ratio of 2.5. This catalyst further exhibited a slight deactivation during a 102 h run with a decrease in the conversion from 100% to 80% due to coke deposition as evidenced by XPS and TGA-MS, resulting in a 36% loss of the specific surface area.

Aquivion®–carbon composites via hydrothermal carbonization: amphiphilic catalysts for solvent-free biphasic acetalization

One-pot hydrothermal carbonization of polysaccharides (i.e. guar gum or cellulose) with Aquivion® perfluorosulfonic superacid at 180 °C produced new amphiphilic Aquivion®–carbon composites. The materials stabilized dodecyl aldehyde/ethyleneglycol Pickering emulsions, and thus efficiently catalyzed the solvent-free biphasic acetalization reaction under moderate conditions with excellent reusability.

Homogeneously-acid catalyzed oligomerization of glycerol

Here we report the screening of various homogeneous acid catalysts in the oligomerization of glycerol at 150 °C. Under optimized conditions, a mixture of oligoglycerol with an average degree of oligomerization of 3.4 was obtained at a glycerol conversion of 80%. At such a conversion, the selectivity to oligoglycerols was higher than 90%. Oligoglycerols were then successfully alkylated, offering an attractive route to valuable molecules (biosurfactants or hydrotropes).

Al‐doped SBA‐15 Catalysts for Low‐temperature Dehydration of 1,3‐Butanediol into Butadiene

SBA‐15 catalysts doped with variable aluminum amounts were prepared through a facile evaporation‐induced self‐assembly process. The textural properties and acidity of the catalysts could be tuned simply by varying the aluminum content. The genesis of acid sites with weak and medium strength during reaction was directly correlated to the catalytic activity for the dehydration of 1,3‐butanediol into butadiene (BD). The best performance was achieved over an Al‐SBA‐15 sample with a silica/alumina ratio of 76, exhibiting a stable BD yield of 59 % at temperatures as low as 200 °C.

Enhancing ethylene epoxidation of a MWW-type titanosilicate/H2O2 catalytic system by fluorine implanting

Fluorine-implanted titanosilicate Ti-MWW, with greatly enhanced catalytic performance in the liquid-phase epoxidation of ethylene with aqueous hydrogen peroxide, has been post-synthesized by fluorinating conventional Ti-MWW with NH4F. The effects of fluorination conditions, such as solvent, the amount of NH4F addition and temperature, on the zeolite structure and the catalytic performance of the resultant fluorine-implanted Ti-MWW were investigated in detail. Methanol proved to be a better solvent for fluorination than water in terms of preserving the crystalline structure and improving the selective epoxidation activity. Fluorine-implanting generated SiO3/2F species in the framework to increase the electropositivity of the tetrahedral Ti active sites. A stronger hydrogen-bond was thus formed between Hend in Ti–Oα–Oβ–Hend intermediates and the adjacent Si–F species, which were helpful to significantly increase the catalytic activity in the epoxidation of ethylene with H2O2. In addition, the fluorination also generated secondary mesopores which are useful to improve the accessibility of the active sites, making the fluorine-implanted Ti-MWW catalyst possess better reusability than the parent one.

A Pd/CeO2 "H2 pump" for the direct amination of alcohols

A Pd/CeO2 catalyst with a prominent reversible H2 storage capacity revealed a high activity and selectivity in the direct amination of benzyl alcohol with aniline and ammonia via the borrowing hydrogen mechanism.