A facile strategy for confining ZnPd nanoparticles into a ZnO@Al2O3 support: A stable catalyst for glycerol hydrogenolysis

Dry solidification of chloride salts and heavy metals in waste incineration fly ash by mayenite

There are hazardous substances such as chloride salts and heavy metals in the municipal solid waste incineration fly ash (WIFA). During thermal treatment, the concentrated chlorides promote the volatilization of heavy metals, increasing the ecological risk. The water washing method is also employed as a pre-treatment for WIFA, but a substantial volume of wastewater with high chloride content is produced that poses challenges for effective treatment. This study integrates chemical stabilization with heat treatment method and suggests the utilization of a calcium aluminum oxide-mayenite (CA) for the solidification of chloride salts and heavy metals in WIFA. The experimental results indicate that adding CA for heat treatment has a significant solidification effect on chlorides. Under the conditions of WIFA: CA mass ratio of 1: 1 and temperature of 1200 °C, the chloride ions were solidified by forming Ca12Al14O32Cl2, with a fixation efficiency of up to 85 %, and most of the chlorides in WIFA became insoluble instead of soluble. Most of the heavy metals in WIFA were immobilized and doped into the crystal structure of CA, forming the catalytic metal-rich Ca12Al14O32Cl2 phase, which was subsequently applied to the degradation of chlorobenzene. Under an initial concentration of 512 ppm, the degradation efficiency of chlorobenzene reached 50.4 %. Through the introduction of CA, not only the solidification of chloride and heavy metals is achieved, but the high-value resource utilization of the final heat treatment product is also realized, providing a new method for the disposal of fly ash.

Heterogeneous Catalysts for Glycerol Biorefineries: Hydrogenolysis to 1,2-Propylene Glycol

Research on the use of biomass resources for the generation of energy and chemical compounds is of great interest worldwide. The development and growth of the biodiesel industry has led to a parallel market for the supply of glycerol, its main by-product. Its wide availability and relatively low cost as a raw material make glycerol a basic component for obtaining various chemical products and allows for the development of a biorefinery around biodiesel plants, through the technological integration of different production processes. This work proposes a review of one of the reactions of interest in the biorefinery environment: the hydrogenolysis of glycerol to 1,2-propylene glycol. The article reviews more than 300 references, covering literature from about 20 years, focusing on the heterogeneous catalysts used for the production of glycol. In this sense, from about 175 catalysts, between bulk and supported ones, were revised and discussed critically, based on noble metals, such as Ru, Pt, Pd, and non-noble metals as Cu, Ni, Co, both in liquid (2-10 MPa, 120-260 °C) and vapor phase (0.1 MPa, 200-300 °C). Then, the effect of the main operational and decision variables, such as temperature, pressure, catalyst/glycerol mass ratio, space velocity, and H₂ flow, are discussed, depending on the reactors employed. Finally, the formulation of several kinetic models and stability studies are presented, discussing the main deactivation mechanisms of the catalytic systems such as coking, leaching, and sintering, and the presence of impurities in the glycerol feed. It is expected that this work will serve as a tool for the development of more efficient catalytic materials and processes towards the future projection of glycerol biorefineries.

Pd-promoting reduction of zinc salt to PdZn alloy catalyst for the hydrogenation of nitrothioanisole

Catalytic hydrogenation of sulfur-containing substrates is an important and challenging reaction in the chemical industry. In this work, active carbon supported PdZn alloy catalyst was prepared by self-reduction method using zinc acetate as precursor without H₂ atmosphere. During the process of self-reduction, Zn²⁺ was firstly reduced to Zn⁰ at 300 °C by active carbon and reducing gas from the decompose of acetate under the promotion of metal Pd, and Zn⁰ further reacted with metal Pd to form PdZn alloy phase at 500 °C. These PdZn/AC-X catalysts showed the higher conversion and stability for the hydrogenation of 4-nitrothioanisole than the Pd/AC-600 catalyst. The excellent catalytic performance of PdZn/AC-600 catalyst can be attributed to formation of PdZn alloy, in which electron-rich Pd atoms weaken the binding ability between Pd and S and enhance the sulfur-resistance of catalyst. On the other hand, H₂-TPR and DFT theory calculation further indicated that the PdZn alloy phase weakens the adsorption capacity of S. Compared with the Pd/AC-600 catalyst, the PdZn alloy phase in PdZn/AC-600 catalyst has not changed and only a small amount of sulfur-containing substrates deposited on the catalyst surface after three cycles. PdZn/AC-600 catalyst exhibited improved stability in the hydrogenation of 4-nitrothioanisole and can be used three cycles with little decrease in activity.

Glycerol Hydrogenolysis with In Situ Hydrogen Produced via Methanol Steam Reforming: The Promoting Effect of Pd on a Cu/ZnO/Al2O3 Catalyst

The glycerol hydrogenolysis to produce 1,2-propanediol without using externally supplied hydrogen was investigated using methanol present in crude glycerol to provide in situ hydrogen via its steam reforming reaction. This paper focuses on the promoting effect of Pd on the reactivity of a Cu/Zn/Al2O3 catalyst. Adding 2 wt% Pd onto a Cu/ZnO/Al2O3 catalyst significantly improved the selectivity to 1,2-propanediol from 63.0% to 82.4% and the glycerol conversion from 70.2% to 99.4%. This enhancement on the catalytic activity by Pd is mainly due to the improved hydrogenation of acetol, which is the intermediate formed during the glycerol dehydration. The rapid hydrogenation of acetol can shift the reaction equilibrium of glycerol dehydration forward resulting in a higher glycerol conversion. The improved reducibility of the catalyst by Pd allows the catalyst to be reduced in situ during the reaction preventing any loss of catalyst activity due to any potential oxidation of the catalyst. The catalyst was slightly deactivated when it was firstly recycled resulting in a 5.4% loss of glycerol conversion due to the aggregation of Cu and the deactivation became less noticeable upon further recycling.

Sulfate-functionalized metal–organic frameworks supporting Pd nanoparticles for the hydrogenolysis of glycerol to 1,2-propanediol

Installing sulfate and Pd in MOF-808 achieved glycerol conversion to 1,2-PDO via selective hydrogenolysis.

Platinum-copper single atom alloy catalysts with high performance towards glycerol hydrogenolysis

Selective hydrogenolysis of biomass-derived glycerol to propanediol is an important reaction to produce high value-added chemicals but remains a big challenge. Herein we report a PtCu single atom alloy (SAA) catalyst with single Pt atom dispersed on Cu nanoclusters, which exhibits dramatically boosted catalytic performance (yield: 98.8%) towards glycerol hydrogenolysis to 1,2-propanediol. Remarkably, the turnover frequency reaches up to 2.6 × 10³ mol_glycerol·mol_PtCu-SAA^-1·h^-1, which is to our knowledge the largest value among reported heterogeneous metal catalysts. Both in situ experimental studies and theoretical calculations verify interface sites of PtCu-SAA serve as intrinsic active sites, in which the single Pt atom facilitates the breakage of central C-H bond whilst the terminal C-O bond undergoes dissociation adsorption on adjacent Cu atom. This interfacial synergistic catalysis based on PtCu-SAA changes the reaction pathway with a decreased activation energy, which can be extended to other noble metal alloy systems.

Advances in porous and nanoscale catalysts for viable biomass conversion

Solid catalysts with unique porosity and nanoscale properties play a promising role for efficient valorization of biomass into sustainable advanced fuels and chemicals.