BACKGROUND An alternative carboxymethyl cellulose‐based biosorbent hydrogel was synthesized by grafting 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) onto the prepared carboxymethyl cellulose backbone via microwave heating. Response surface methodology was employed to optimize the hydrogel synthesis condition for maximum gel content with respect to AMPS dose, N,N′‐methylene‐bis‐acrylamide dose, and microwave exposure time. The prepared gels were then characterized and evaluated in terms of their heavy metal ions adsorption performance and reusability. RESULTS The optimum synthesis condition yielded the maximum gel content and maximum equilibrium swelling of 96.33% and 2819 ± 15%, respectively. The Langmuir model fitted the experimental isotherm data well, with maximum adsorption capacity of 86.21, 102.04 and 33.56 mg g‐1 for Cu2+, Pb2+ and Fe3+, respectively. Microwave heating was clearly noted to result in hydrogel of higher porosity and could shorten the synthesis time by 88.33%; the gel content was 7.46% higher compared with that obtained via conventional heating. CONCLUSION Microwave‐assisted heating is a feasible alternative and an efficient technique for CMC‐g‐AMPS hydrogel synthesis. The optimized CMC‐g‐AMPS hydrogel exhibited good performance for Cu2+, Pb2+ and Fe3+ ions removal and was satisfactorily reused, thus contributing to the alleviation of environmental problems caused by discarded rice straw and water contaminated with heavy metal ions. © 2017 Society of Chemical Industry

Deactivation of catalysts due to rapid blocking of active surfaces and pores is a major problem for methane cracking. The removal of the template using different calcination methods contributes to the different characteristics of catalyst support. Therefore, silica supports were prepared with the sol–gel method, where sodium silicate and chitosan are a silica source and a template, respectively. Calcination using a microwave muffle furnace (MWF) was preferred over the conventional electric muffle furnace at the heating rates of 2 and 17 °C/min (CEF2 and CEF17, respectively) in order to remove the chitosan template. A nickel nitrate precursor was loaded onto the obtained silica supports by the incipient wetness impregnation method. The properties of the silica support and the Ni/SiO2 catalysts were characterized by means of N2-sorption, X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray, field emission transmission electron microscopy, and H2 temperature-programmed reduction. The catalytic activity was evaluated using a fixed-bed reactor at 550 °C with a CH4/N2 ratio of 1:4 in the feed. The amount and the allotropes of carbon deposited on the spent catalysts were investigated using thermogravimetric/differential thermal analysis. The results showed that the SiO2-MWF support had a higher surface area and a larger pore volume of a mesoporous structure with larger interparticle channels than that of the SiO2-CEF supports. This leads to the higher dispersion of Ni metal particles over and inside the interparticle channels of the SiO2-MWF support. This provided a higher metal–support interaction, resulting in lower rates of methane conversion and carbon deposition on the catalyst surface than those of Ni/SiO2-CEF catalysts. However, it displayed a lower bed pressure. It was found that the carbon fibers deposited on all the catalysts were multiwalled carbon nanotubes (MWCNTs). Additionally, the base-growth mechanism of MWCNTs was only exhibited by the Ni/SiO2-MWF catalyst.

Ni-Ce-Zr-Oδ catalysts were prepared via one-pot hydrothermal synthesis. It was found that Ni can be partially incorporated into the Ce-Zr lattice, increasing surface oxygen species. The catalysts possess high surface areas even at high Ni loadings. The catalyst with Ni content of 71.5 wt.% is able to activate CO2 methanation even at a low temperature (200 °C). Its CO2 conversion and methane selectivity were reported at 80% and 100%, respectively. The catalyst was stable for 48 h during the course of CO2 methanation at 300 °C. Catalysts with the addition of medium basic sites were found to have better catalytic activity for CO2 methanation.

Thermal treatment during catalyst preparation is one of the important factors affecting the characteristics and performance of a catalyst. To improve the catalytic performance of an alumina-supported copper catalyst prepared by an impregnation method for dimethyl ether (DME) synthesis from CO 2 , the effects of the use of hot air and infrared drying as well as calcination at 600 and 900°C to prepare alumina supports were investigated. Infrared drying could shorten the required drying time by 75% when compared with hot air drying. Infrared drying could also help maintain the pore size and pore volume of the supports, leading to their larger surface areas. Different drying techniques were additionally noted to result in different sizes and shapes of the pores as well as to different copper distributions and intensities of acid sites of the catalyst. An increase in the calcination temperature resulted in a decrease in the surface area of the supports because of particle aggregation. The drying technique exhibited a more significant effect than calcination temperature on the spacetime yield of DME. A catalyst utilizing the support prepared by infrared drying and then calcined at 600°C exhibited the highest yield of DME (40.9 g DME kg cat −1 h −1 ) at a reaction temperature of 300°C. Stability of the optimal catalyst, when monitored over a 24 h period, was noted to be excellent.

BACKGROUND Oxidative coupling of methane (OCM) is a promising catalytic process for the conversion of methane to higher‐valued hydrocarbons (C2+). In this study, Na2WO4‐TiO2‐MnOx/SiO2 (NWTM) catalysts were obtained by various treatment techniques, including conventional calcine (CC, 800 °C), cold plasma (CP, 7 kV, 1 Hz), microwave radiation (MW, 800 °C), and electron beam radiation (EB, 4000 kGy), with no surface treatment (WT) as a benchmark method. RESULTS The results showed substantial differences in catalytic performance. The catalyst prepared by the cold plasma method provided the highest performance in the activity (20.91% C2+ yield with 48.04% C2+ selectivity and 43.52% CH4 conversion) at the early stage of testing (1–4 h). CONCLUSION However, the catalyst prepared by microwave radiation achieved the most stable active phases for the 24‐h testing period and yielded the highest C2+ for a five‐cycle reusability test. The catalyst prepared by electron beam radiation was found to have the lowest C2+ activity due to the poor distribution of the active elements. © 2021 Society of Chemical Industry (SCI).