5 research outputs found
Heterogeneously Catalyzed Hydroprocessing of Organosolv Lignin in Sub- and Supercritical Solvents
A highly effective method for catalytic hydroprocessing of lignin to liquid products has been developed in supercritical ethanol (scEtOH) medium at moderate reaction conditions. The problems associated with the low lignin conversion (<20%) and char formation at higher temperatures in hot compressed water (HCW) were overcome in scEtOH. A significant increase in the calculated āhigher heating valueā (HHV) of the formed liquid was observed in a reaction using a heterogeneous catalyst compared to a reaction without a catalyst. The liquid product contains mainly substituted phenols, such as guaiacols and syringols, as major components. On the basis of the product distribution, a possible reaction pathway for the formation of the phenolic products is described. A maximum HHV up to 36.2 MJ/kg was calculated for a product obtained over 5% Ru/Ī³-Al<sub>2</sub>O<sub>3</sub> at 300 Ā°C after 20 h of reaction time. Lignin conversion of ca. 98% was observed. The yield for the liquid product reached values up to 92%
Steady-State and Transient Kinetic Studies of the Acetoxylation of Toluene over PdāSb/TiO<sub>2</sub>
A combination
of steady-state catalytic tests, transient studies
with isotopic tracers, and kinetic modeling was used to derive detailed
insights into the individual reaction pathways in the course of toluene
acetoxylation over a PdāSb/TiO<sub>2</sub> catalyst. This reaction
can be considered as an environmentally friendly route for the production
of benzyl alcohol. Benzyl acetate and benzaldehyde are the only products
formed from toluene, while acetic acid gives CO<sub>2</sub> in addition
to benzyl acetate. The Arrhenius plots revealed apparent activation
energies for formation of benzyl acetate and benzaldehyde of 24.9
and 27.5 kJ mol<sup>ā1</sup>, respectively, thus, indicating
that these products originate from the same surface intermediate,
i.e. benzyl cation. The corresponding value for CO<sub>2</sub> formation
was 152.9 kJ mol<sup>ā1</sup>. Transient isotopic studies and
their kinetic evaluation demonstrated the participation of lattice
oxygen and adsorbed oxygen species in activation of acetic acid, with
the latter species favoring oxidation of the acid to CO<sub>2</sub>
Ternary VZrAlON Oxynitrides - Efficient Catalysts for the Ammoxidation of 3āPicoline
Starting from previous binary VZrON
(VAlON) oxynitrides with high
(low) activity and low (high) selectivity, a new class of ternary
VZrAlON catalysts has been developed for the ammoxidation of 3-picoline
to 3-cyanopyridine (3-CP), which combine the beneficial properties
of the binary oxynitrides, leading to improved selectivity at retained
high activity and to the highest space-time yield of 3-CP ever measured
(488 g L<sup>ā1</sup> h<sup>ā1</sup>). This is attributed
to the formation of a special āā”āV<sup>5+</sup>(O)āNāAlĀ(Zr)ā surface moiety consisting of a
V<sup>5+</sup>ī»O species in the vicinity of a surface nitrogen
and an anion vacancy occupied by an electron, which is supposed to
provide optimum conditions for a double Marsāvan Krevelen mechanism
comprising activation of gas-phase oxygen and ammonia via reversible
incorporation into the catalyst surface as well as an efficient electron
transport
Selective Catalytic Reduction of NO<sub><i>x</i></sub> of Ship Diesel Engine Exhaust Gas with C<sub>3</sub>H<sub>6</sub> over Cu/Y Zeolite
Various
solid Cu-containing catalysts were prepared. Their performance
in the selective catalytic reduction of NO<sub><i>x</i></sub> using propene as reducing agent from 150 to 450 Ā°C in an O<sub>2</sub>-rich model exhaust gas in the presence of water vapor was
investigated. This research aimed at the development of a catalytic
NO<sub><i>x</i></sub> to N<sub>2</sub> (DeNO<sub><i>x</i></sub>) step to be part of a ship diesel exhaust abatement
system in combination with other techniques, such as nonthermal plasma.
Among the catalysts tested, Cu on zeolite Y with an optimized load
of 16 wt % (denoted as 16Cu/Y) displayed excellent DeNO<sub><i>x</i></sub> activity with highest selectivity toward N<sub>2</sub> at 290 Ā°C. The influence of other variables, such as Cu load,
calcination temperature, feed composition, and GHSV on the performance
of 16Cu/Y was studied, as well. The highest N<sub>2</sub> yield of
98% was achieved using 2000 ppm of propene in the gas feed. The presence
of O<sub>2</sub> proved to be a crucial factor for promoting the selective
reduction of NO<sub><i>x</i></sub> with C<sub>3</sub>H<sub>6</sub> over this catalyst. On the other hand, the presence of water
in the feed decreased NO<sub><i>x</i></sub> to N<sub>2</sub> conversion. However, the catalyst showed excellent stability over
120 h, even at high water concentration, and also after repeated heating
from ambient temperature to 450 Ā°C, and it was reusable after
downtimes without remarkable loss in activity. The nature of the Cu
species was studied by XPS, XRD, and TPR experiments
Hierarchical ZSMā5 Materials for an Enhanced Formation of Gasoline-Range Hydrocarbons and Light Olefins in Catalytic Cracking of Triglyceride-Rich Biomass
A hierarchical ZSM-5 material with
a high fraction of mesoporosity
coupled to well-preserved intrinsic zeolite characteristics has been
successfully prepared by postsynthesis modifications involving optimization
of base treatment and subsequent strong acid washing of commercial
Al-rich ZSM-5 (parent ZSM-5). The resulting hierarchical ZSM-5 material
was thoroughly characterized before being tested in the cracking of
triglyceride-rich biomass, i.e., model feedstock triolein and real
feedstock waste cooking oil under fluid catalytic cracking conditions.
The results show that the introduction of intracrystalline mesoporosity
enhances the utilization of zeolite acid sites by the enlarged external
surface, leading to an increased conversion. At the same time, it
partially suppresses the undesired secondary reactions by shortening
micropore diffusion path lengths. With such a hierarchical ZSM-5 material,
higher selectivities toward the desired products, i.e., gasoline-range
hydrocarbons and light olefins, than with commercial ZSM-5 have been
achieved