Chemical Circular Economy

Hydrodeoxygenation of Bio-Oil to Alkanes

Bio-oil, produced by the destructive distillation of cheap and renewable lignocellulosic biomass, contains high energy density oligomers in the water-insoluble fraction that can be utilised for diesel and valuable fine chemicals productions. Here we show a highly active and stable hydrodeoxygenation (HDO) catalyst that combines atomically-dispersed Pd on a mixed-valent Mo5/6+ oxide phosphate on silica (Pd/m-MoO3-P2O5/SiO2). Using a wood and bark derived feedstock, Pd/m-MoO3-P2O5/SiO2 performs hydrodeoxygenation of lignin, cellulose and hemicellulose-derived oligomers into liquid alkanes with high efficiency and yield. Using phenol as a model substrate this catalyst is 100% effective and 97.5% selective for hydrodeoxygenation to cyclohexane under mild conditions, showing no decrease in catalytic performance after 63 hours under continuous flow operation. Detailed investigations into the nature of the catalyst shows it combine exceptionally high both Brønsted and Lewis acidic sites and facile Mo redox characteristics, we believe these are key features for the efficient catalytic hydrodeoxygenation behaviour.

Characterisation of the Pd/m-MoO3-P2O5/SiO2 catalyst. a, High-angle annular dark-field scanning transmission electron microscopy image of Pd/m-MoO3-P2O5/SiO2. Inset shows the size distribution of the clusters. Scale bar equals 20 nm. b, Aberration-corrected annular-bright-field scanning transmission electron microscope image and c, corresponding high-angle annular dark-field scanning transmission electron microscopy image of Pd/m-MoO3-P2O5/SiO2. Scale bars equal 5 nm. d, STEM-EDS elemental mapping results for Pd/m-MoO3-P2O5/SiO2, showing a homogeneous distribution of the elements within clusters. Scale bar equals 3 nm

Catalytic performance on hydrodeoxygenation of phenol. a, Comparison of different catalysts at 383 K, 1 Mpa H2 for two hours in batch reaction. Reaction conditions: phenol (0.195 mmol), catalyst (including 0.00045 mmol Pd), decalin (7 mL), reaction mixture stirred at 800 rpm. b, Long-term stability test on the Pd/m-MoO3-P2O5/SiO2 at 453 K, 1 MPa H2 with a weight hourly space velocity of 0.085 h-1 in a continuous flow reaction. 

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Green Packaging 

One of the major challenges in the circular economy relating to food packaging is the elimination of metallised film which is currently the industry standard approach to achieve the necessary gas barrier performance. Here, we report the synthesis of high aspect ratio 2D non-toxic layered double hydroxide (LDH) nanosheet dispersions using a non-toxic exfoliation method in aqueous amino acid solution. High O2 and water vapour barrier coating films can be prepared using food safe liquid dispersions through a bar coating process. The oxygen transmission rate (OTR) of 12 μm PET coated film can be reduced from 133.5 cc·m−2·day−1 to below the instrument detection limit (<0.005 cc·m−2·day−1). The water vapour transmission rate (WVTR) of the PET film can be reduced from 8.99 g·m−2·day−1 to 0.04 g·m−2·day−1 after coating. Most importantly, these coated films are also transparent and mechanically robust, making them suitable for flexible food packing while also offering new recycling opportunities.

We report a method to rationally control the aspect ratio of layered double hydroxide for use as a barrier coating for food packaging films. The reconstruction of a Mg2Al-layered double oxide (LDO) in concentrated aqueous glycine solutions produces dispersions of Mg2Al-LDH nanosheets. The nanosheet thickness decreases and diameter increases with increasing reconstruction time from 16 to 96 h. We observe a limiting nanosheet aspect ratio of ca. 336 ± 170. These Mg2Al-LDH nanosheets can be dispersed in PVA to give a water-based dispersion that can be used to coat flexible polymeric films. Oxygen transmission rate (OTR) of a PET film decreases when the thickness of the dried coated layer increases, an OTR of <0.005 mL·m–2·day–1 is observed for a coating with thickness of 1175 ± 101 nm.

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Lactide Polymerisation

Of the variety of biodegradable polymers known, linear aliphatic polyesters are particularly attractive and most used, especially those derived from lactic acid (PLA). Lactic acid can be obtained by fermentation of renewable resources such as corn and sugar beets and was the first synthetic polymer to be produced from annually renewable resources.



A series of group 3, 4 and 13 permethylindenyl chrloride, aryloxide, and borohydride complexes have been synthesised and fully characterised. Their activities for the ring-opening polymerisation (ROP) of L-, D-, meso- and rac-lactide have been tested. The ROP of L- and rac-lactide produced isotactic polylactide (PLA) and moderately heterotactic PLA (Pr = 0.68–0.72), respectively. Good agreement between experimental and theoretical molecular weights of PLA (Mn) and relatively narrow dispersities were obtained. 

Few initiators displayed second order dependence on monomer concentration and produced isotactic and heterotactic (Pr = 0.81) polylactides for the polymerisation of L-, D- and rac-lactide respectively. The effects of temperature, catalyst concentration, co-initiator concentration, solvent and scale were studied. 









A family of group 4 alkoxide and aryloxide complexes of a chiral cyclopentadienyl-derived (hydro)permethylpentalenyl ligand (C8Me6H; Pn*(H)) have been prepared and fully characterised. Both racemic and enantiopure complexes of all group 4 congeners were prepared with a wide variety of alkoxide and aryloxide ligands. The complexes were investigated as initiators for the ring-opening polymerization of L- and rac-lactide in order to ascertain if these mixtures of diastereomers could exert any stereocontrol on the resulting polymerization. Kinetic studies were completed to explore the effects of the metal cation, chiral (hydro)permethylpentalenyl ligand, ancillary ligands, initiator concentration and temperature. Both Pn*(H)Zr(S–OCH{CH3}C6H5)3 and Pn*(H)Zr(rac-OCH{CH3}C6H5)3 demonstrated very high rates of propagation for l- and rac-lactide (1.885 < kobs < 3.442 h–1) at 100 °C. 








A family of well-defined cyclopentadienyl and indenyl group 4 complexes has been prepared. The complexes were investigated as catalysts for the polymerization of L- and rac-lactide. (Ind)2ZrMe(OtBu) was shown to be the fastest catalyst. At 100 °C, the rates of polymerization (kobs) for L- and rac-lactide were very similar (0.317 and 0.293 h−1 respectively). However, at 80 °C it was found that polymerization of L-LA (kobs = 0.217 h−1) was twice as fast as rac-LA (kobs = 0.120 h−1).







A family of group 4 permethylpentalene complexes, Pn*MCpRX (M = Ti, Zr; CpR = Cp, CpMe, CptBu, CpnBu, CpMe3, Ind; X = Cl, Me) has been synthesised and fully characterised by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction studies. The effect of substitution around the Cp ligand was examined for ethylene polymerisation

A series of group 4 complexes η5-Pn*(H)TiCl3, [η5-Pn*(H)ZrCl3]2 and [η5-Pn*(H)HfCl3]2 containing a η5-permethylpentalene ligand were prepared by the reaction of η5-Pn*(H)SnMe3 with the corresponding group 4 starting materials. The complexes initiated ring opening polymerisation of L- and rac-lactide.










A series of bis(peralkylindenyl)zirconocene and hafnocene complexes were synthesised and characterised by NMR spectroscopy, mass spectrometry and elemental analyses.

We report the synthesis of two zirconocenes, dimethylsilylbis(hexamethylindenyl) zirconium dichloride, rac-(SBI*)ZrCl2, and nbutyldimethylsilyl(hexamethylindenyl) zirconium trichloride, [(Ind*SiMe2nBu)Zr(μ-Cl)Cl2]2. The complexes were characterised by NMR spectroscopy and X-ray crystallography, and the bonding was evaluated using density functional theory. 

The synthesis and characterisation of constrained geometry scandium and aluminium permethylindenyl complexes Me2SB(RN,I*)ScCl(THF), Me2SB(iPrN,I*)Sc(O-2,6-iPr-C6H3)(THF), Me2SB(iPrN,I*)Sc(O-2,4-tBu-C6H3)(THF), Me2SB(nBuN,I*)Sc(O-2,6-iPr-C6H3)(THF), Me2SB(PhN,I*)Sc(O-2,6-iPr- C6H3)(THF), Me2SB(tBuN,I*)AlCl(THF), Me2SB(tBuN,I*)Al(O-2,6-Me-C6H3)(THF) and Me2SB(tBuN,I*)Al(O-2,4-tBu-C6H3)(THF) are reported. Ring-opening polymerisation of L- and rac-lactide using all complexes show first-order dependence on monomer concentration and produced polylactide with unimodal molecular weight distribution. 


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