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This research focused on the reaction features and kinetics of tar catalytic conversion by char based on the generation and evolution of gas products. To probe the roles of heat and catalysis in tar conversion, a micro fluidized bed reaction analyzer (MFBRA) was used to assess tar thermal cracking (TC) and catalytic cracking (CC) by char at 1073, 1123, 1173, and 1223 K. The tar cracking behavior of the individual gas components (H 2 , CO, CO 2 , and CH 4), generation rates, and reaction kinetics were thoroughly investigated. The results show that TC and CC included a fast (Stage-1) and slow (Stage-2) conversion stage, in which Stage-1 contributed more than 80% of the total conversion. Compared to TC, tar CC required a longer reaction time but obtained higher conversions to individual gas components and the total gas products. The final conversion ratios (X CC/TC) of H 2 , CO, CO 2 , and CH 4 were kept above 1 at the tested temperature. The char catalytic action was very remarkable, especially at low temperatures. In tar CC, the generation rate of individual gas components slowly declined after quickly reaching the peak, forming a relatively stable zone. The volume reaction model (VRM) well described the tar conversion behavior with and without char. Compared to TC, char lowered the activation energy (Ea) of gas generation. For individual gas components (H 2 , CO, CO 2 , CH 4) and the total gas products, the corresponding reduction degree of Ea was 25.56%, 24.18%, 22.14%, 4.75%, and 21.71%, respectively, further displaying the promoting impact of char. The evaluated generation features and kinetics of individual components in the gas products will benefit the in-situ tar removal in the biomass gasification process. • Tar thermal and catalytic cracking were assessed on a micro fluidized bed reaction analyzer. • Test was based on real-time analysis of gas products rather than tar mass change. • Gas components were mainly generated in the initial stage of tar thermal and catalytic cracking. • Char played an essential role in the initial conversion process even in low temperature. [ABSTRACT FROM AUTHOR]

In this study, a micro fluidized bed reaction analyzer (MFBRA) was used to investigate the reaction characteristics of tar thermal cracking and steam reforming at different temperatures (T, 750, 850, and 950 °C) and steam partial pressures (SP, 10%, 20%, and 30%). The reaction kinetics, including gas components generation (H 2 , CO, CO 2 , and CH 4) and carbon (C) conversion in gas products, were calculated and further compared. For the two processes, the behaviors of gas generation and C conversion can be classified as Stage-1 and Stage-2 based on the different increases. By raising temperature and SP, the yields of H 2 /CO/CH 4 and C conversion increased obviously, while CO 2 showed a growing and subsequently declining trend. A similar phenomenon also existed in the relationship between reaction rate Vs. gas yield/C conversion. Compared to thermal cracking, the reaction time in tar steam reforming became much longer; the yields of H 2 /CO/CH 4 and the C conversion increased significantly, while CO 2 decreased. In the meantime, there was a clear reduction in all reaction rates of gas generation and C conversion. Furthermore, in tar steam reforming, the activated energy (Ea) of gas components generation (H 2 , CO, CO 2 , and CH 4) decreased from 114.92 to 90.48, 86.54–74.49, 32.39–28.87, and 55.34–42.06 kJ/mol, respectively; and Ea of total C conversion lowered from 87.74 to 65.75 kJ/mol. Additionally, SP had no impact on Ea during tar steam reforming. To ensure the validity of the test results by MFBRA, the kinetics of tar thermal cracking was compared with that in the literature. • Tar thermal cracking and steam reforming were conducted on MFBRA. • Characteristics and kinetics of gas product release and C conversion were compared. • Tar steam reforming had higher tar conversion to gas, lower reaction rate and Ea. • Accuracy of kinetics was analyzed by comparing with the results in literature. [ABSTRACT FROM AUTHOR]

• Catalytic role of char's Fe 2 O 3 and K 2 O in tar cracking were assessed on a micro fluidized bed reaction analyzer. • Reaction characteristics and kinetics were analyzed based on gas products release and evolution. • Fe 2 O 3 displayed better catalytic activity in tar conversion than K 2 O. In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char's inherent Fe 2 O 3 and K 2 O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe 2 O 3 - and K 2 O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer's high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe 2 O 3 and K 2 O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K 2 O at 1173 K, Fe 2 O 3 -loaded char promoted the generation of H 2 , CO, CO 2 , CH 4 , C 3 H 6 , and the total gas products with the conversion ratio (X Fe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C 2 H 6 with the X Fe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO 2 , CH 4 , and the total gas products improved to different extent. During tar catalytic cracking, Fe 2 O 3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH 4 , H 2 , CO, CO 2 , C 3 H 6 and the total gas products by Fe 2 O 3 -loaded char further decreased drastically and that of C 2 H 6 increased obviously. All of these indicated the catalytic activity of the inherent Fe 2 O 3 in char was better than K 2 O. [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, an urchin-like Fe 2 O 3 @In 2 S 3 hybrid composite is designed and synthesized using a facile process. The composite efficiently harvests light in both the ultraviolet and visible regions, and the unique hierarchical structure provides several advantages for photocatalytic applications: (i) a suitable band-matching structure and broadband-light absorbing capacity enable the reduction of CO 2 into hydrocarbon, (ii) the extensive network of interfacial contact between nano-sized Fe 2 O 3 and In 2 S 3 significantly increases the separation of charge carriers and enhances the utilization of photogenerated electron-hole pairs, and (iii) an abundance of surface oxygen vacancies provide numerous active sites for CO 2 molecule adsorption. The optimized Fe 2 O 3 @In 2 S 3 composite generated CO from the photocatalytic reduction of CO 2 at a rate of 42.83 μmol·g−1·h−1, and no signs of deactivation were observed during continued testing for 32 h under 300 W Xe lamp irradiation. [ABSTRACT FROM AUTHOR]

Hollow ZnO@ZnS core-sheath heterojunction photocatalyst exhibits approximately 100% CO selectivity and excellent stability for CO 2 reduction reaction, resulting from the hollow core-sheath structure enhancing light capture and absorption, exposing more effective active sites, as well as the heterostructure between ZnO and ZnS improving the separation efficiency of charge carriers. [Display omitted] • Hollow ZnO@ZnS core-sheath heterojunction was successfully synthesized by combining radio frequency thermal plasma and hydrothermal treatment technology. • The intermediate of hollow ZnO@ZnS core-sheath heterojunction was captured and the formation mechanism was proposed and verified. • The ZnO@ZnS photocatalyst with optimal S/Zn molar ratio exhibits approximately 100% CO selectivity and excellent stability. • The hollow core-sheath heterostructure can enhance light capture and absorption, expose more effective active sites and build a type-II heterojunction between ZnO and ZnS to improve the separation efficiency of charge carriers. The utilization of solar energy to convert CO 2 into small energy molecules is a potential "carbon neutral" technology for CO 2 emission reduction. However, the industrial application is significantly constrained due to the low reduction efficiency, complexity of the synthesis methods, and limitations in scaling up the catalyst materials. In this work, we have successfully designed and synthesized a series of hollow tubular ZnO@ZnS core-sheath heterostructured materials, by combining radio-frequency thermal plasma and hydrothermal treatment technologies. The S:Zn molar ratio, reaction time, and temperature were systematically investigated, and the morphology of intermediate products was successfully captured, which provided conclusive evidence for the proposed formation mechanism. Notably, the photocatalytic CO yield of the ZS 0.5 O hollow nanotube core-sheath composite is not only 3.20 or 4.03 times higher than that of the pure ZnO or ZnS, respectively, but also possesses excellent stability. By in-depth characterization, we found that the hollow core-sheath heterostructure enhances light capture and absorption, exposes more effective active sites, and builds a type-II heterojunction between ZnO and ZnS to enhance the separation efficiency of charge carriers. The synergy of these factors significantly improves the catalytic performance, offering new insights for photocatalytic, electrocatalytic, and photoelectrocatalytic CO 2 reduction. [ABSTRACT FROM AUTHOR]