Search

Lignin valorization and particularly its depolymerization into bio‐aromatics, has emerged as an important research topic within green chemistry. However, screening of catalysts and reaction conditions within this field is strongly constrained by the lack of analytical techniques that allow for fast and detailed mapping of the product pools. This analytical gap results from the inherent product pool complexity and the focus of the state‐of‐the‐art on monomers and dimers, overlooking the larger oligomers. In this work, this gap is bridged through the development of a quasi‐orthogonal GPC‐HPLC‐UV/VIS method that is able to separate the bio‐aromatics according to molecular weight (hydrodynamic volume) and polarity. The method is evaluated using model compounds and real lignin depolymerization samples. The resulting color plots provide a powerful graphical tool to rapidly assess differences in reaction selectivity towards monomers and dimers as well as to identify differences in the oligomers. [ABSTRACT FROM AUTHOR]

A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed by the stable commercial resin Lewatit K2629, for which a turnover frequency (TOF) of 6.2 ± 0.4 × 10−3 s−1 was obtained. The absence of temperature and concentration gradients was verified with correlations and experimental tests. The potential for assessing the deactivation of a catalyst was demonstrated by a second intrinsic kinetics evaluation where a methylaminopropyl (MAP)-functionalized mesoporous silica catalyst was used for the aldol reaction of acetone with 4-nitrobenzaldehyde in different solvents. The cooperative MAP catalyst deactivated as a function of time on stream when using hexane as solvent. Yet, the monofunctional MAP catalyst exhibited stable activity for at least 4 h on stream, which resulted in a TOF of 1.2 ± 0.1 × 10−3 s−1. It did, however, deactivate with dry acetone or DMSO as solvent due to the formation of site-blocking species. This deactivation was mitigated by co-feeding 2 wt % of water to DMSO, resulting in stable catalyst activity. [ABSTRACT FROM AUTHOR]

• The leaching behaviour and mechanisms are elucidated via combined data analysis. • A homogeneous-heterogeneous catalytic system prevails for both NP catalysts. • The leaching pathway critically depends on the resin functionality. • Phenylpalladium(II)hydroxide complexes are proposed as the leached Pd2+ species. The Pd leaching behaviour of a strongly acid (Lewatit K2629) versus strongly basic (Lewatit MP500 OH) ion exchange resin supported Pd nanoparticle (Pd-NP) catalyst is elucidated in the Suzuki reaction between iodobenzene and phenylboronic acid with K 2 CO 3 as base in 1:1 (v/v) DMF/H 2 O at 40 °C. Reaction and leaching kinetic analyses combined with hot filtration tests indicated heterogeneous-homogeneous catalysis for both Pd-NP catalysts. More particularly, leaching experiments showed that for Pd-NP Lewatit K2629, Pd-NP as well as molecular Pd2+ leaching (as phenylpalladium(II)hydroxide complexes) occurred due to, respectively, the disturbance of the electrostatic NP stabilization by dissociated K 2 CO 3 and reaction with iodobenzene and hydroxide. For Pd-NP Lewatit MP500 OH, however, molecular Pd2+ leaching induced by iodobenzene, dominates. Hence, the resin functionality determines the contribution of each leaching pathway. Furthermore, at high conversions, Pd re-deposition occurred due to the decreased amount of leaching inducing reagents causing enlarged NPs in the resin which leached less in subsequent runs. [ABSTRACT FROM AUTHOR]

The effect of Ba, Ce, Cs and La as co-metals in Cu/γ-Al 2 O 3 catalysts for the hydrogenolysis of glycerol into 1,2-propanediol was investigated at industrially relevant reaction conditions over time. The addition of Ba or Ce increased the initial activity per Cu0 accessible site. Apart from Cs, the co-metals increased the selectivity towards 1,2-propanediol, up to 96% (Ba). The co-metals inhibited sintering and stabilized the Cu particle size during reaction, by decreasing the particle growth by a factor of 10. Overall, co-metals mainly influenced the selectivity and stabilized the Cu particle. Unlabelled Image • Ba-, Ce-, Cs- and La-doping stabilized the Cu0 particle size during the reaction. • Doping with Ba, Ce or Cs preserved the initial glycerol conversion. • Comparable 1,2-propanediol productivities to commercial catalyst wwas achieved under continuous liquid flow operation. • A selectivity of 96% for 1,2-propanediol was achieved with the Ba-doped catalyst. [ABSTRACT FROM AUTHOR]