Two-Dimensional Layered Double Hydroxide Derived from Vermiculite Waste Water Supported Highly Dispersed Ni Nanoparticles for CO Methanation

Biochar-layered double hydroxide composites for the adsorption of tetracycline from water: synthesis, process modeling, and mechanism

Antibiotic-contaminated water is a crucial issue worldwide. Thus, in this study, the MgFeCa-layered double hydroxides were supported in date palm-derived biochar (B) using co-precipitation, hydrothermal, and co-pyrolysis methods. It closes gaps in composite design for pharmaceutical pollutant removal, advances eco-friendly adsorbents, and advances targeted water cleanup by investigating synthesis methodologies and gaining new insights into adsorption. The prepared B-MgFeCa composites were investigated for tetracycline (TC) adsorption from an aqueous solution. The B-MgFeCa composites synthesized through co-precipitation and hydrothermal methods exhibited better crystallinity, functional groups, and well-developed LDH structure within the biochar matrix. However, the co-pyrolysis method resulted in the LDH structure breakage, leading to the low crystalline composite material. The maximum adsorption of TC onto all B-MgFeCa was obtained at an acidic pH range (4-5). The B-MgFeCa composites produced via hydrothermal and co-pyrolysis methods showed higher and faster TC adsorption than the co-precipitation method. The kinetic results can be better described by Langmuir kinetic and mixed order models at low and high TC concentrations, indicating that the rate-limiting step is mainly associated with active binding sites adsorption. The Sip and Freundlich models showed better fitting with the equilibrium data. The TC removal by B-MgFeCa composites prepared via hydrothermal, the highest estimated uptake which is around 639.76 mg.g-1 according to the Sips model at ambient conditions, and co-pyrolysis was mainly dominated by physical and chemical interactions. The composite obtained via the co-precipitation method adsorbed TC through chemical bonding between surface functional groups with anionic species of TC molecule. The B-MgFeCa composite showed excellent reusability performance for up to five cycles with only a 30% decrease in TC removal efficiency. The results demonstrated that B-MgFeCa composites could be used as promising adsorbent materials for effective wastewater treatment.

Synthesis of Propylene Carbonate by Urea Alcoholysis—Recent Advances

Organic carbonates are considered the chemicals of the future. In particular, propylene carbonate is widely used as a non-reactive solvent, plasticizer, fuel additive, and reagent, especially in the production of environmentally friendly polymers that are not harmful to human health. This paper reviews recent literature findings regarding the development of propylene carbonate synthetic methods starting from propane-1,2-diol and urea. The ammonia formed during the synthesis is recycled to obtain urea from carbon dioxide.

Defect-Rich Nickel Nanoparticles Supported on SiC Derived from Silica Fume with Enhanced Catalytic Performance for CO Methanation

With the increased demands of environmental protection, recycling/utilization of industrial byproducts has attracted much attention from both industry and academic communities. In this work, silicon carbide (SiC) was successfully synthesized from industrial waste silica fume (SF) during metallic silicon production. Following this, Ni nanoparticles with many defects were supported on the as-obtained SiC by conventional impregnation method. The results showed that defect-rich Ni nanoparticles were dispersed onto the surface of SiC. The as-obtained Ni/SF-SiC exhibited an enhanced metal-support interaction between Ni and SiC. Furthermore, the density functional theory (DFT) calculations showed that the H2 and CO adsorption energy on Ni vacancy (VNi) sites of Ni/SF-SiC were 1.84 and 4.88 eV, respectively. Finally, the Ni/SF-SiC performed high catalytic activity with CO conversion of 99.1% and CH4 selectivity of 85.7% at 350 °C, 0.1 MPa and a gas hourly space velocity (GHSV) of 18,000 mL·g−1·h−1. Moreover, Ni/SF-SiC processed good catalytic stability in the 50 h continuous reaction.

Highly Dispersed Ni Nanocatalysts Derived from NiMnAl-Hydrotalcites as High-Performing Catalyst for Low-Temperature Syngas Methanation

Increasing the low-temperature performance of nickel-based catalysts in syngas methanation is critical but very challenging, because at low temperatures there is high concentration of CO on the catalyst surface, causing formation of nickel carbonyl with metallic Ni and further catalyst deactivation. Herein, we have prepared highly dispersed Ni nanocatalysts by in situ reduction of NiMnAl-layered double hydroxides (NiMnAl-LDHs) and applied them to syngas methanation. The synthesized Ni nanocatalysts maintained the nanosheet structure of the LDHs, in which Ni particles were decorated with MnOy species and embedded in the AlOx nanosheets. It was observed that the Ni nanocatalysts exhibited markedly better low-temperature performance than commercial catalysts in the syngas methanation. At 250 °C, 3.0 MPa and a high weight hourly space velocity (WHSV) of 30,000 mL·g−1·h−1, both the CO conversion and the CH4 selectivity reached 100% over the former, while those over the commercial catalyst were only 14% and 76%, respectively. Furthermore, this NiMnAl catalyst exhibited strong anti-carbon and anti-sintering properties at high temperatures. The enhanced low-temperature performance and high-temperature stability originated from the promotion effect of MnOy and the embedding effect of AlOx in the catalyst.

High CO Methanation Performance of Two-Dimensional Ni/MgAl Layered Double Oxide with Enhanced Oxygen Vacancies via Flash Nanoprecipitation

As a methanation tool, two-dimensional (2D) carrier-loaded Ni has attracted the attention of many researchers. We successfully prepared 2D MgAl layered double oxides (LDO) carriers via flash nanoprecipitation (FNP). Compared to the LDO samples prepared by conventional co-precipitation (CP), the 2D MgAl-LDO (FNP) has more oxygen vacancies and more exposed active sites. The Ni/MgAl-LDO (FNP) catalyst demonstrates a CO conversion of 97%, a CH4 selectivity of 79.8%, a turnover frequency of 0.141 s−1, and a CH4 yield of 77.4% at 350 °C. The weight hourly space velocity was 20,000 mL∙g−1∙h−1 with a synthesis gas flow rate of 65 mL∙min−1, and a pressure of 1 atm. A control experiment used the CP method to prepare Ni/MgAl-LDO. This material exhibits a CO conversion of 81.1%, a CH4 selectively of 75.1%, a TOF of 0.118 s−1, and a CH4 yield of 61% at 450 °C. We think that this FNP method can be used for the preparation of more 2D LDO catalysts.

Two-Dimensional Layered Double Hydroxides for Reactions of Methanation and Methane Reforming in C1 Chemistry

CH₄ as the paramount ingredient of natural gas plays an eminent role in C1 chemistry. CH₄ catalytically converted to syngas is a significant route to transmute methane into high value-added chemicals. Moreover, the CO/CO₂ methanation reaction is one of the potent technologies for CO₂ valorization and the coal-derived natural gas production process. Due to the high thermal stability and high extent of dispersion of metallic particles, two-dimensional mixed metal oxides through calcined layered double hydroxides (LDHs) precursors are considered as the suitable supports or catalysts for both the reaction of methanation and methane reforming. The LDHs displayed compositional flexibility, small crystal sizes, high surface area and excellent basic properties. In this paper, we review previous works of LDHs applied in the reaction of both methanation and methane reforming, focus on the LDH-derived catalysts, which exhibit better catalytic performance and thermal stability than conventional catalysts prepared by impregnation method and also discuss the anti-coke ability and anti-sintering ability of LDH-derived catalysts. We believe that LDH-derived catalysts are promising materials in the heterogeneous catalytic field and provide new insight for the design of advance LDH-derived catalysts worthy of future research.