Andrei N. Parvulescu

Chemical Imaging of Catalyst Deactivation during the Conversion of Renewables at the Single Particle Level: Etherification of Biomass-Based Polyols with Alkenes over H-Beta Zeolites

The etherification of biomass-based alcohols with various linear alpha-olefins under solvent-free conditions was followed in a space- and time-resolved manner on 9 microm large H-Beta zeolite crystals by confocal fluorescence microscopy. This allowed us to visualize the interaction with the substrate and distribution of the coke products into the catalyst at the level of an individual zeolite crystal during the etherification process. The spectroscopic information obtained on the micrometer-scale zeolite was in line with the results obtained with bulk characterization techniques and further confirmed by the catalytic results obtained both for micrometer-scale and nanoscale zeolites. This allowed us to explain the influence of the substrate type (glycerol, glycols, and alkenes) and zeolite properties (Si/Al ratio and particle size) on the etherification activity. The etherification of the biomass-based alcohols takes place mainly on the external surface of the zeolite particles. The gradual blockage of the external surface of the zeolite results in a partial or total loss of etherification activity. The deactivation could be attributed to olefin oligomerization. The high conversions obtained in the etherification of 1,2-propylene glycol with long linear alkenes (up to 80%) and the pronounced deactivation of the zeolite observed in the etherification of glycerol with long linear alkenes (max. 20% conversion) were explained by the spectroscopic measurements and is due to differences in the adsorption, i.e., in the center of the zeolite particle for glycerol and on the external surface in the case of glycols.

Telomerization of 1,3-butadiene with various alcohols by Pd/TOMPP catalysts: new opportunities for catalytic biomass valorization

The telomerization of 1,3-butadiene with various alcohols has been investigated using a catalyst based on a Pd(acac)2 precursor and a phosphine ligand, TOMPP (TOMPP = tris-(o-methoxyphenyl)phosphine). We were able to demonstrate the capability of the catalyst to telomerize 1,3-butadiene with various multifunctional nucleophiles having primary and secondary alcohol functions. High yields of telomer products (>98%) were obtained in very short reaction times (<2 h). The telomerization activity and selectivity of the Pd/TOMPP complex was strongly influenced by the type of alcohol used as substrate. When diols were used, telomerization of 1,3-butadiene with 1,2-propanediol and 1,2-butanediol afforded the highest yield of mono-telomer (over 70%) and for 1,2-butanediol a turnover frequency (TOF) of 300 000 h−1 was reached, combined with a turnover number (TON) of 7800.

Tracing Catalytic Conversion on Single Zeolite Crystals in 3D with Nonlinear Spectromicroscopy

The cost- and material-efficient development of next-generation catalysts would benefit greatly from a molecular-level understanding of the interaction between reagents and catalysts in chemical conversion processes. Here, we trace the conversion of alkene and glycol in single zeolite catalyst particles with unprecedented chemical and spatial resolution. Combined nonlinear Raman and two-photon fluorescence spectromicroscopies reveal that alkene activation constitutes the first reaction step toward glycol etherification and allow us to determine the activation enthalpy of the resulting carbocation formation. Considerable inhomogeneities in local reactivity are observed for micrometer-sized catalyst particles. Product ether yields observed on the catalyst are ca. 5 times higher than those determined off-line. Our findings are relevant for other heterogeneous catalytic processes and demonstrate the immense potential of novel nonlinear spectromicroscopies for catalysis research.

Facile Access to Key Reactive Intermediates in the Pd/PR3‐Catalyzed Telomerization of 1,3‐Butadiene

The Pd-catalyzed telomerization of 1,3-dienes is an important atom-efficient transformation, which effectively adds nucleophiles (NuH, for example, H2O, MeOH, NH3) over two C C coupled dienes in a 1,6- or 3,6-fashion (see Scheme 1).[1] As such, telomerization provides an economically attractive route for the production of C8 bulk chemicals, such as 1- octanol[2] and 1-octene.[3] Pd-catalyzed telomerization is also increasingly explored as a potential route for the valorization of biomass-derived feedstock.[1a] Although the catalytic cycle (Scheme 1) is generally regarded as well understood, only a limited number of studies have been reported that involve the preparation of reactive intermediates.[4–6] Clearly cumbersome preparative methods and the poor stability of [Pd(1,2,3,8-h4-octadien-1,8-diyl)- (PR3)] (B) are limiting further study. As a result the preparation of reactive intermediates derived from commercially relevant ligands (e.g. TPPTS; TPPTS=3,3’,3’’-phosphinidynetris( benzenesulfonic acid) trisodium salt) remains elusive.[7] B mainly acts as a base on NuH during catalysis and is readily converted into [Pd(1,2,3,7,8-h5-octa-2,7-dien-1- yl)(PR3)]+ (C)[4–5] and its derivatives. Both from a synthetic and catalytic point of view, C is the key intermediate as it lies at the focal point of the catalytic cycle and leads via several mechanistic pathways to species such as D, E, and F.

Mechanistic Study of the Pd/TOMPP‐Catalyzed Telomerization of 1,3‐Butadiene with Biomass‐Based Alcohols: On the Reversibility of Phosphine Alkylation

Liquid‐chromatography electrospray‐ionisation mass spectrometry (LC‐ESI‐MS) studies on reaction mixtures of the telomerization of 1,3‐butadiene with biomass‐based polyols revealed that the TOMPP (TOMPP=tris(2‐methoxyphenyl)phosphine) ligand is converted towards the corresponding (2,7‐octadienyl)phosphonium species during catalysis. The extent of ligand alkylation is substrate dependent and was identified as the primary cause of deactivation for carbohydrate substrates with anomeric hydroxyl groups. Coordination studies of the phosphonium cation with [Pd(dba)2] (dba=dibenzylideneacetone) gave insight into the alkylation mechanism and showed that the formation of the phosphonium cation is fully reversible. The reaction yields the key cationic intermediate [Pd(1,2,3,7,8‐η5‐octa‐2,7‐dien‐1‐yl)(TOMPP)]+, which, in the presence of the iodide anion, results in the formation of [Pd(1,2,3‐η3‐octa‐2,7‐dien‐1‐yl)(I)(TOMPP)]. Both complexes were fully characterized by various techniques including single crystal X‐ray crystallography. Based on these results, an extension to the Pd/TOMPP‐catalyzed telomerization mechanism was formulated to include the 2,7‐octadienylphosphonium cation as a ligand reservoir. Catalytic tests show that the use of [Pd(dba)2] as precatalyst improves the telomerization of glucose and xylose.

Investigation of glycerol polymerization in the clinker grinding process

Concrete production is a large scale process that involves high energy consumption. In order to increase the sustainability of this process, the reduction of energy input is necessary. Bio-glycerol was demonstrated to be a highly efficient renewable-based additive in the grinding process for concrete production and helped reduce energy costs and improve the quality of the resulting product. In order to understand its excellent aiding properties, the interaction of glycerol with cement clinkers was investigated; both chemical and physical interactions were taken into account. The results of this investigation points to surface tension modification of the clinker particles as one of the main effects of bio-glycerol addition during the grinding process.