In order to reduce considerable emissions of Ncontaining pollutants from combustion of sewage sludge derived solid fuel, an integrated system of hydrothermal deamination and air stripping was developed to effectively remove and recover nitrogen from dewatered sewage sludge (DSS). Three characteristic hydrothermal regimes contributing to deamination were identified. Initial hydrolysis of inorganic-N and labile protein-N was responsible for ammonium (NH 4 + -N) released below 300 °C/9.3 MPa, whereas deamination of pyridine-N dominated when being raised to 340 °C/15.5 MPa. At 380 °C and 22.0 MPa, remarkable deamination of stable protein-N occurred, which was accompanied by formation of more heterocyclic-N compounds and resulted in 76.9% N removal from DSS and 7980 mg/L NH 4 + -N solution. As a result of catalytic hydrolysis and cracking, calcium oxide additive not only accelerated deamination of stable protein-N, pyrrole-N, and pyridine-N, but also favored transformations of protein-N and quaternary-N to nitrile-N and pyridine-N, respectively, leading to 86.4% total N removal efficiency. The nitrogen transformation reactions and conversion pathways during hydrothermal deamination were proposed and elaborated in detail. Moreover, an efficient air stripping process was coupled to remove and recover ammonia from liquid fraction via ammonium sulfate. Consequently, this system achieved an overall N recovery rate of 62%.
To
investigate metal oxide surface catalysis, determining an appropriate
Hubbard U-correction term is a challenge for the
density functional theory (DFT) community and identifying realistic
reaction intermediates and their corresponding X-ray photoelectron
spectroscopy (XPS) shifts is a challenge for experimental researchers,
when these methods are used independently. In this study, using CuO
as a model transition metal oxide, we demonstrate that when DFT and
XPS are applied synergistically, the determination of the U value and the identification of adsorbate/intermediate
species on the surface (and their XPS shifts) can be done simultaneously.
The experimental O 1s spectra of the as-synthesized CuO 2D-nanoleaves
shows the presence of four different peaks with core level binding
energies (CLBEs) of 529.7, 531.4, 533.2, and 534.6 eV. DFT is used
to calculate the CLBE shifts for probable adsorbed moieties, in various
adsorption configurations, on both, clean and vacancy defect containing
surfaces. Comparison of experimental and theoretical CLBEs across
the entire U value range of 0–9 eV narrows
down the list to only four moieties, namely, O2 in the
η1(O) configuration, H2O at the surface
oxygen vacancy site, and adsorbed HCO3 and HCO2 (resembling adsorbed HCO3). Finally, the U value of 4–4.5 eV reproduces the experimental CLBE shifts
correctly and thus, establishes these experimental XPS spectral peaks
to the adsorbates and their geometries. The integrated approach elucidated
in this article, results in the identification of adsorbates/intermediates
(and their CLBEs) for the experimental XPS spectral analysis and the
determination of an appropriate U value concurrently,
to study metal oxide surface catalysis.
An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl C-H bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of C-C cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates.
We report here, and rationalize, a synergistic effect between a non-noble metal oxide catalyst (CuO) and high frequency ultrasound (HFUS) on glucose oxidation. While CuO and HFUS are able to independently oxidize glucose to gluconic acid, the combination of CuO with HFUS led to a dramatic change of the reaction selectivity, with glucuronic acid being formed as the major product. By means of DFT calculations, we show that, under ultrasonic irradiation of water at 550 kHz, the surface lattice oxygen of a CuO catalyst traps H• radicals stemming from the sonolysis of water, making the ring opening of glucose energetically non-favorable and leaving a high coverage of •OH radical on the CuO surface which selectively oxidize glucose to glucuronic acid. This work also points towards a path to optimize the size of the catalyst particle for an ultrasonic frequency which minimizes the damage to the catalyst, resulting in its successful reuse.
Glycerol was oxidized selectively to oxalic and tartronic acids in 78% yield over a highly crystalline CuO catalyst prepared within a few minutes by a sonochemical synthesis.
A novel Pd-based catalyst hosted over a nitrogen enriched fibrous porous-organic-polymer with a high density of step sites and exhibits versatile catalytic performance over different types of vegetable oils to furnish long chain diesel-range alkanes.
Titania‐supported gold nanoparticles were prepared by using the deposition–precipitation method, followed by reduction under a hydrogen flow. The catalytic activity of these as‐prepared catalysts was explored in the oxidation of cellobiose to gluconic acid with molecular oxygen, and the properties of these catalysts were examined by using XRD, TEM, temperature‐programmed desorption of NH3, energy‐dispersive X‐ray spectroscopy, UV/Vis, and X‐ray photoemission spectroscopy (XPS). The catalyst sample reduced at high temperature demonstrated an excellent catalytic activity in the oxidation of cellobiose. The characterization results revealed the strong metal–support interaction between the gold nanoparticles and titania support. Hydrogen reduction at higher temperatures (usually >600 °C) plays a vital role in affording a unique interface between gold nanoparticles and titania support surfaces, which thus improves the catalytic activity of gold/titania by fine‐tuning both the electronic and structural properties of the gold nanoparticles and titania support.
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