Ultrasonically assisted surface modified CeO2 nanospindle catalysts for conversion of CO2 and methanol to DMC

Ordered versus Non-Ordered Mesoporous CeO2-Based Systems for the Direct Synthesis of Dimethyl Carbonate from CO2

In this work, non-ordered and ordered CeO2-based catalysts are proposed for CO2 conversion to dimethyl carbonate (DMC). Particularly, non-ordered mesoporous CeO2, consisting of small nanoparticles of about 8 nm, is compared with two highly porous (635-722 m2/g) ordered CeO2@SBA-15 nanocomposites obtained by two different impregnation strategies (a two-solvent impregnation method (TS) and a self-combustion (SC) method), with a final CeO2 loading of 10 wt%. Rietveld analyses on XRD data combined with TEM imaging evidence the influence of the impregnation strategy on the dispersion of the active phase as follows: nanoparticles of 8 nm for the TS composite vs. 3 nm for the SC composite. The catalytic results show comparable activities for the mesoporous ceria and the CeO2@SBA-15_SC nanocomposite, while a lower DMC yield is found for the CeO2@SBA-15_TS nanocomposite. This finding can presumably be ascribed to a partial obstruction of the pores by the CeO2 nanoparticles in the case of the TS composite, leading to a reduced accessibility of the active phase. On the other hand, in the case of the SC composite, where the CeO2 particle size is much lower than the pore size, there is an improved accessibility of the active phase to the molecules of the reactants.

Ultrasound probe enhanced enzymatic hydrolysis for rapid separation of β2-adrenergic agonists from animal urine and livestock wastewater: Applicability to biomonitoring investigation

BACKGROUND

An increasing number of β2-adrenergic agonists are illicitly used for growth promoting and lean meat increasing in animal husbandry in recent years, but the development of analytical methods has lagged behind these emerging drugs.

RESULTS

Here, we designed and developed an ultrasound probe enhanced enzymatic hydrolysis reactor for quick separation and simultaneously quantification of 22 β2-adrenergic agonists in animal urine and livestock wastewater. Owing to the enhancement of the conventional enzymatic digestion through the ultrasound acoustic probe power, only 2 min was required for the comprehensively separation of β2-adrenergic agonists from the sample matrices, making it a much more desirable alternative tool for high-throughput investigation. The swine, bovine and sheep urines (n = 287), and livestock wastewater (n = 15) samples, collected from both the north and south China, were examined to demonstrate the feasibility and capability of the proposed approach. Six kinds of β2-adrenergic agonists (clenbuterol, salbutamol, ractopamine, terbutaline, clorprenaline and cimaterol) were found in animal urines, with concentrations ranged between 0.056 μg/L (terbutaline) and 5.79 μg/L (clenbuterol). Up to nine β2-adrenergic agonists were detected in wastewater samples, of which four were found in swine farms and nine in cattle/sheep farms, with concentration levels from 0.069 μg/L (tulobuterol) to 2470 μg/L (clenbuterol).

SIGNIFICANCE

Interestingly, since β2-adrenergic agonists are usually considered to be abused mainly in the pig farms, our data indicate that both the detection frequencies and concentrations of these agonists in the ruminant farms were higher than the pig farms. Furthermore, the findings of this work indicated that there is a widespread occurrence of β2-adrenergic agonists in livestock farms, especially for clenbuterol and salbutamol, which may pose both food safety and potential ecological risks. We recommend that stricter controls should be adopted to prevent the illegally usage of these β2-adrenergic agonists in agricultural animals, especially ruminants, and they should also be removed before discharging to the environment.

Influence of Synthesis Conditions on Catalytic Performance of Ni/CeO2 in Aqueous-Phase Hydrogenolysis of Glycerol without External Hydrogen Input

The aqueous-phase hydrogenolysis of glycerol was studied in Ni/CeO2 catalytic systems prepared by incipient wetness impregnation. The operating conditions were 34 bar, 227 ºC, 5 wt.% of glycerol, and a W/mglycerol = 20 g catalyst min/g glycerol without a hydrogen supply. The effect of the catalyst preparation conditions on the catalytic activity and physicochemical properties of the catalysts was assessed, particularly the calcination temperature of the support, the calcination temperature of the catalyst, and the Ni content. The physicochemical properties of the catalysts were determined by N2 adsorption, H2-TPR, NH3-TPD, and XRD, among other techniques. A relevant increase in acidity was observed when increasing the nickel content up to 20 wt.%. The increase in the calcination temperatures of the supports and catalysts showed a detrimental effect on the specific surface area and acid properties of the catalysts, which were crucial to the selectivity of the reaction. These catalysts notably enhanced the yield of liquid products, achieving global glycerol conversion values ranging from 17.1 to 29.0% and carbon yield to liquids ranging from 12.6 to 24.0%. Acetol and 1,2-propanediol were the most abundant products obtained in the liquid stream.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.