## 留言板

Effects of calcium content on the performance of HZSM-5 nanoparticles of 150 nm with Si/Al ratio = 230 in the methanol to olefin conversion were investigated. The parent and modified catalysts showed their largest yields of ethylene and propylene at 490 ͦ C and lower WHSV (= 3.3 h−1). The selectivity for propylene over HZSM-5 was 0.45 at 490 °C whereas it was promoted to 0.51 over Ca27-HZSM-5 (Ca/Al = 27). With decreasing temperature from 490 to 440, and 390 °C, the yield of propylene and ethylene remained nearly constant at 0.13−0.14 and 0.10−0.11 over Ca27-HZSM-5, respectively; more narrow than the corresponding range of yields for HZSM-5 (0.10−0.14 and 0.08−0.12). FT-IR results confirmed the formation of oxygenated and poly alkyl aromatic species in the carbon deposits. TG results indicated that oxygenate coke was formed and converted to heavier poly aromatic coke species with time. Increasing Ca in the porous structure of HZSM-5 may lead to heavier aromatic carbonaceous deposits. In general, Ca content positively affected activity through modification of the density, strength, and accessibility of Brønsted and Lewis acid sites. Long-term MTO activity test of HZSM-5 with Ca/Al = 27 showed stable performance over 100 h, although with an oscillatory feature.

Recently, the disposal of waste by beneficial and environmentally friendly methods has attracted great attention. In this work, we have studied the production of high-value carbon nanotubes (CNTs) which have remarkable applications by catalytic pyrolysis of sugarcane bagasse (SCB) as an agricultural waste using a two-stage process. Various reaction factors including the effects of zeolite catalysts (HZSM-5, HMOR, and HY), pyrolysis temperatures (450−700 °C), and SCB/ZSM-5 ratios (3−12) on SCB pyrolysis were investigated to generate CNTs from pyrolysis products. A Co-Mo/MgO catalyst was used for growing CNTs via the decomposition of pyrolysis products. The morphological structure and quality of CNTs were characterized using TEM and Raman spectroscopy, while the fresh Co-Mo/MgO catalyst was characterized by XRD and TPR analyses. The results showed that zeolite type, pyrolysis temperature, and SCB/ZSM-5 ratio had significant effects on the CNTs yield. The optimum carbon yield (24.9 wt%) was achieved using the HZSM-5 catalyst at the pyrolysis temperature of 500 °C and with the SCB/ZSM-5 ratio of 6. TEM observations confirmed the growth of bamboo-like carbon nanotubes (BCNTs) and carbon nano-onions (CNOs) in different proportions according to the reaction parameters. Also, CNTs with the largest diameter distribution range (7−76 nm) were produced using the SCB/ZSM-5 ratio of 6. Raman spectra demonstrated the production of high-quality CNTs under all studied conditions

Electrocatalytic water splitting is one of the most prospective technology for hydrogen production. Molybdenum disulfide (MoS2), as one of the most promising non-noble metal electrocatalysts, suffers from the disadvantages of limited catalytic sites and weak conductivity which urgently needs to be further optimized. Herein, the C3N4-Ti4O7-MoS2 heterostructure is constructed through a simple hydrothermal strategy. The interfacial interaction between the active components leads to more exposed active sites, the redistribution of the surface charge, the optimization of the hydrogen adsorption kinetics and stability, which makes up the typical shortcomings of MoS2. The results indicate that the interface effect endows C3N4-Ti4O7-MoS2 catalyst with excellent electrocatalytic activity for hydrogen evolution reaction (HER). The current density of 50 mA/cm2 for HER is obtained at the overpotential of 300 mV, with the lower Tafel slope (54 mV/dec) and stable catalytic activity over 33 h, which is much better than that of the pure MoS2. This work indicates that the interface effect, as an effective strategy for rational design of MoS2-based electrocatalysts, is crucial to the future development of catalytic hydrogen production.

The isomerization and hydroformylation of butene under the catalysis of Rh-BIPHEPHOS were investigated by varying the butene feed and reaction temperature. The results indicate that in the presence of syngas, with 1-butene as feed, more isomerization product (i.e. 2-butene) is detected in comparison with the hydroformylation products, whereas with 2-butene as the feed, the hydroformylation was superior to isomerization. Due to the equilibrium limit between 1-butene and 2-butene, the increase of temperature shows a great positive effect on the isomerization reaction. Furthermore, under the catalysis of Rh-BIPHEPHOS, more n-pentanal is always formed than i-pentanal, as the larger bite angle of BIPHEPHOS restricts the intermediate rearrangement in the formation of i-pentanal.

Waste gasification has the potential to contribute to China’s transition towards carbon neutrality and zero waste cities via the recirculation of waste as secondary carbon feedstock for the production of chemicals with lower/and or zero carbon footprint, green hydrogen with zero carbon footprint and CO2-neutral synthetic liquid fuels. With China’s significant coal gasification capacity and associated experiences and expertise, Coal-to-X could act as a bridge to Waste-to-X for carbon intensive sectors such as the waste management, chemical production and mobility sectors. To illustrate the opportunities in these areas, this article presented highlights from dynamic global developments in waste gasification, focusing on pioneering industrial developments in Germany between 1980’s−2000’s as well as current international developments. Lessons learnt from previous and current waste gasification project deployment are shared and enabled the identification of problems which will have to be addressed in the transition from coal gasification towards mono-waste gasification technologies. Additionally, a qualitative evaluation of gasification technologies pointed to the strengths and weaknesses of fixed-bed, fluidized-bed and entrained-flow gasification principles in their application for waste gasification.

The chemical and mineralogical characteristics of fly ash from a municipal solid waste incineration (MSWI) in China and the influence of processing parameters on heavy metals removal during leaching were investigated in this work. The fly ash particles had complex surface structure with limited specific surface area. The alkali chloride and metal salts in MSWI fly ash showed evidently impact on leaching efficiency. Metal leachability was related to their properties and speciation in fly ash. Water-soluble salts such as KCl, NaCl and CaCl2 in fly ash were easily washed out. In this study, removal efficiency by water washing was achieved to 93.1% for Cl, 41.4% for Na, 48.5% for K and 24.8% for Ca, respectively. Mineralogical analysis also revealed change of fly ash mineral phases and specification distribution after water washing. Under liquid to solid ratio of 40∶1 L/kg and treatment time of 120 min, the leaching process achieved high dropping yields of toxicity characteristic leaching procedure (TCLP) concentrations for Cu, Zn Cd and Pb (80%−100%), moderate dropping yields for As (30%−80%) and relatively low dropping yields of Ni (< 30%). In addition, heavy metals such as Pb and Zn in fly ash with twice water washing treatment at a low liquid-solid ratio could reach lower TCLP concentrations. The result indicated that the combination process of twice water washing and one acid washing could significantly reduce the environmental risk of MSWI fly ash.

The effect of desulfurizer, modified TiO2 prepared by different methods on the NO emission from inferior coal burning and the adaptability of coal type were studied by using a tube furnace. The prepared Zr-TiO2 and the char were characterized by XRD, BET, SEM, XPS, TGA and XRF, and the mechanism of denitrification was explored. The results show that the addition of desulfurizer can promote NO emission. When the combustion temperature is 850℃, oxygen flow rate is 40 mL/min and the desulfurizer is MgO, the NO emission is the lowest as the catalyst of 5%Zr-TiO2 prepared by impregnation method is added, which is 51.0% lower than that with addition of pure TiO2 and 84.6% lower than that with pure coal under the same conditions. The catalyst 5% Zr-TiO2 can be applied to the coal with sulfur < 3% and ash < 30%, having a wide application range . The doping of Zr can inhibit the growth of grain, enhance the active component, increase the content of adsorbed oxygen, promote the transformation of the valence states of the elements, accelerate the devolatilization of volatiles, promote the combustion, increase the specific surface area of chars, and enhance the ability of heterogeneous reduction of chars.

A series of metal phosphides including MoP, WP, CoP and NiP was prepared by temperature-programmed reduction with hydrogen from different phosphorus precursors. The effect of phosphorus precursor and feed H2/CO ratio on the catalytic performance of metal phosphides in the methanation was investigated. In comparison with diammonium hydrogen phosphate (DAP), phytic acid (PA) as a chelating agent can effectively disperse the metal precursor, reduce the reduction temperature, promote to form pure phosphide phase, and give the phosphide catalyst a higher surface area and a smaller particle size; as a result, the metal phosphides prepared with PA as a phosphorus precursor exhibit higher catalytic activity in methanation. In addition, the catalytic activity of various metal phosphides in methanation follows the sequence of MoP > WP > CoP > NiP. A high H2/CO ratio in the feed is favorable for the methanation over the phosphide catalysts; the selectivity to methane increases with an increase in the H2/CO ratio.