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To study the effect of anion in sodium salts on catalytic gasification and provide some useful information for the recovery and reutilization of catalysts, the catalytic reactivity of Na2CO3, Na2SO4, NaNO3 and NaCl was compared. In addition, the melting process of catalyst, mineral composition, specific surface area and CO2 adsorption ability of chars loaded with catalyst was measured by in situ hot stage microscope, XRD, BET and TGA. Moreover, the mineral transformations of catalytic gasification ash were also investigated by FactSage. The results indicate that anions in sodium salts have a significant effect on gasification. Among them, Na2SO4 and Na2CO3 can greatly accelerate the catalytic gasification rate of coal char. The char loaded with Na2SO4 or Na2CO3 shows more specific surface area and more adsorption capacity of CO2 than other chars. Simultaneously, the pictures captured by hot stage microscope reveal that Na2SO4 and Na2CO3 melt, become liquid film and then spread over char surface and neighboring particles; this facilitates the contact between carbon and catalyst and accelerates the gasification reaction. Na2SO4 is suitable for catalytic gasification from the aspects of its catalytic activity and convenience of recovery and reutilization. [ABSTRACT FROM AUTHOR]

• CH 4 yield increased by 6.46 times with increasing pressure. • Steam promoted H 2 formation but inhibited CH 4 formation. • KCe catalyst increased carbon conversion from 57.07% to 95.40%. • The order of catalytic performance of catalysts was KCe > KCo > KFe > KNi. • KFe and KCo favors water-gas-shift while KNi favors gasification reactions. The effects of temperature, pressure, steam ratio and K-based composite catalysts on the pressurized steam gasification of sawdust char were studied and the physicochemical structure of composite catalysts was characterized in detail. The results indicated that steam promoted the production of hydrogen but suppressed that of CH 4. The generation of CH 4 required high pressure, low temperature and suitable steam atmosphere. The composite catalysts reduced the reaction temperature and increased the carbon conversion, theirs catalytic performance ranked in descending order was KCe > KCo > KFe > KNi, where KCe showed perfect catalytic performance, which mainly determined by the ability to activate carbon during pressurized steam gasification of char. KFe and KCo were more conducive to water-gas-shift reaction, while KNi had the better performance on gasification reaction. The transformation paths of the composite catalysts were as follows: Ce(NO 3) 3 ·6H 2 O → CeO 2 , Co(NO 3) 2 ·6H 2 O → CoO/Co 3 O 4 → Co → CoO, Fe(NO 3) 3 ·9H 2 O → Fe 2 O 3 → FeO → Fe 3 O 4 and Ni(NO 3) 2 ·6H 2 O → NiO → Ni. [ABSTRACT FROM AUTHOR]

In this work, CO 2 catalytic gasification was applied to the utilization of coal gangue (CG). The differences between Na 2 CO 3 and Na 2 SO 4 catalysts on the effects of the catalytic and activation reaction were evaluated comprehensively. Gasification reactivity and aluminum extraction yield were improved in the presence of both alkali metal salts and increased with increasing temperature at 800–1000 °C. The minerals species in Na 2 SO 4 loaded ash (SCA) varied a lot from 800 °C to 850 °C, and the extraction yield can reach the peak (91.39%) at 850 °C. The aluminum ions solution obtained from SCA was purer than that from Na 2 CO 3 loaded ash (CCA), this was owing to that SCA has more compact Si–O bond than CCA. What's more, according to the DFT results, Na 2 SO 4 had a stronger ability to lengthen the Al–O bond and activate the aluminum in minerals. Besides these, it was found that the sodium in SCA was more favorable for accelerating gasification in theory. This research will contribute to the realization of high-value utilization of CG and Na 2 SO 4. [Display omitted] • The concept of using Na 2 SO 4 to activate coal gangue is put forward innovatively. • Na 2 SO 4 has a good effect on gasification process and activation of minerals at 850–900 °C. • The activation mechanism of minerals in coal gangue was discussed. • New interpretation of alkali metals' effect in the catalytic gasification process. [ABSTRACT FROM AUTHOR]

• KCo catalyst increased carbon conversion from 14.38% to 99%. • The order of catalytic performance of catalysts was KCo > KNi > KFe > KCe. • CO 2 adsorption stability was related to the weak adsorption quantity of CO 2. • Gasification reactivity was related to the strong adsorption of CO 2 and catalytic activity. • Gasification mechanisms of Co, Ni, Fe were different from that of CeO 2. Gasification of renewable biomass, sawdust char in this study, was carried out with CO 2 to observe the effect of the gasification temperature, CO 2 adsorption, and K-modified transition metal composite catalysts; this was known as the Boudouard reaction. The catalysts were characterized using inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, BET surface area analysis, and scanning electron microscopy. The reaction mechanism of the catalytic gasification was investigated using thermogravimetry and density functional theory. The results showed that temperature was one of the most important operating variables for char gasification, and carbon conversion increased 2.55 times within 40 min when the temperature increased from 750 °C to 800 °C. Composite catalysts effectively improved the char conversion at low temperatures, and the order of catalytic performance was KCo > KNi > KFe > KCe. The catalytic CO 2 gasification activity depended not only on the CO 2 quantity adsorbed, but also on the CO 2 decomposition activity on the catalyst surfaces. The CO 2 reaction mechanism over Co, Ni, and Fe surfaces can be written as follows: M + CO 2 → M-Oads + CO, M-Oads + C* → M + CO. Over CeO 2 surface, the reaction mechanism was the following: CeO 2 + C* → CeO 2 vacO + CO, CeO 2 vacO + CO 2 → CeO 2 + CO. These results can aid in the CO 2 catalytic gasification mechanism and provide further theoretical guidance to improve the industrialization of biomass gasification. [ABSTRACT FROM AUTHOR]

K-modified transition metal composite catalysts facilitate tremendously the production of methane from sawdust char in high-pressure catalytic steam hydrogasification. [Display omitted] • The order of gasification activity was KNi > KCo > KFe > KCe > raw char; • Catalysts reduced the graphitization degree of char and improved the gasification activity; • Pressure was a necessary condition for obtaining CH 4 ; • Transition metals existed in the form of simple substance except CeO 2 ; • The possible reaction paths and mechanism of gasification were proposed. To achieve high CH 4 concentration, gasification of renewable energy biomass char was carried out with the mixed pressured gasification of steam and hydrogen, considering the effects of temperature, operation pressure, K-modified transition metal composite catalysts, and gasification agents on the carbon conversion and gas yield, especially CH 4 yield. Meanwhile, reaction mechanism of catalytic gasification was investigated. The results showed that gasification activity of samples ranked in descending order was KNi loaded char > KCo loaded char > KFe loaded char > KCe loaded char > raw char. The catalysts reduced the graphitization degree of char and improved the gasification activity. XRD, XPS and Raman indicated the lower the graphitization degree and the less the ordered structure of char was observed after adding catalysts. XRD and FITR manifested that the transition metals existed in the form of simple substance except CeO 2. According to the above results, the possible reaction paths of gasification were proposed, which elucidated the reasons for the increase of CH 4 yield. These results will offer certain instruction and reference significance for steam hydrogasification mechanism of biomass char and provide theoretical guidance and preparation for the industrialization of biomass gasification to produce CH 4 and avoid CO 2 generation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The order of gasification activity was KNi > KCo > KFe > KCe > raw char; • Pressure dominated the position of the highest point of instantaneous CH 4 yield; • Possible transformation pathways of Ni were as follows: Ni(NO 3) 2 ·6H 2 O → NiO → Ni; • The CxNi structure lowered the activation barrier for the ring opening reaction; • Catalyst changed reaction pathways and the most energy-consuming step of reaction. The utilization of biomass char was hindered by the low gasification activity due to thick ring structures and unclear gasification mechanism. Herein, the mechanism was elucidated by experimental and DFT to improve the activity. The results demonstrated that temperature increased the gasification activity but did not changed the order of gasification activity of samples. Pressure dominated the position of the highest point of instantaneous CH 4 yield, and high pressure enhanced carbon conversion by 81.72 % and 7.32 times. Moreover, KNi exhibited an uppermost catalytic activity with the instantaneous CH 4 yield 1.89 times higher than that of raw char at 750 °C. The formation of the CxNi structure lowered the activation barrier for the ring opening reaction. Possible transformation pathways of Ni species were as follows: Ni(NO 3) 2 ·6H 2 O → NiO → Ni. KNi changed the reaction pathways and the most energy-consuming step. The study could shed light on the hydrogasification reaction mechanism. [ABSTRACT FROM AUTHOR]

The effect of added coal ash on the gasification behavior of corn stalk char by using the thermalgravimetric analysis and a lab-scale horizontal fixed bed furnace was investigated. For comparison, synthetic ash with different chemical composition was used for studying the effect of difference ash composition on promoting/inhibiting the gasification reactivity. The results show that the slagging-control preferred coal ash additive has a negative impact on the gasification performance. Interestingly, a relatively less slagging-control preferred coal ash additive has a beneficial impact on promoting the gasification performance under low gasification temperature. This could be due to the difference composition between the two coal ash additives, where the former coal ash type has much lower content in the calcium and iron. In addition, the findings in the synthetic ash suggest that iron can have a better performance in promoting gasification than calcium/magnesium. Two types of coal ash show an inhibiting effect under higher temperature due to temperature might be the dominant factor and the restraining effect of additive. These observations are also supported by the evolution of char structure by using the Raman spectroscopy. Further, the modified random pore model can correlate well with the gasification kinetics data. • Two coal ashes were used to evaluate its effect on biomass gasification reactivity. • The minerals in coal ash play an important role on biomass gasification reactivity. • Iron have better performance in promoting gasification than calcium/magnesium. • Temperature become the key factor to effect the reactivity after 1223 K. • The trend of coal ash effect on char structure change is same with that on reactivity. [ABSTRACT FROM AUTHOR]

• Carbothermal reaction is favorable for wetting behavior between residual char and ash. • Increase of Si/Al and low graphitization degree of char improve wettability of char and ash. • The quantitative relation between wrapped temperature and property of slag and char is established. • Kinetics equations of carbothermal reaction of FeSi and SiC are established. Due to low gasification reactivity of carbon feedstock and improper discharge operation, residual char is often found in bath of moving bed slagging gasifier, which affects the carbon conversion and slag discharge significantly. Moreover, the critical condition of interaction between char and slag determines whether char can be wrapped and consumed by slag in bath, while kinetics of interaction affects consumption rate of residual char wrapped by slag. In this work, the critical condition and kinetics of interaction between residual char and slag were investigated in terms of wetting behavior and carbothermal reaction. Results show that the increase of temperature not only lowers the contact angle between the slag and char, but also be beneficial to carbothermal reaction, thus, high temperature can improve wetting behavior at the slag/char interface. According to different factors that affect wettability during heating, the curve of contact angle between char and ash can be divided into three stages. Besides, it was found that the coal char with low graphitization degree is easy to be wrapped by ash with high SiO 2 /Al 2 O 3 ratio, and quantitative relation between wrapped temperature and property of slag and char was established to predict critical condition of interaction. In addition, a limit of carbothermal reaction in thermodynamics was observed, and non-isothermal kinetic equations of carbothermal reaction were established, which can provide guidance for slag discharge operation of moving-bed slagging gasifier. [ABSTRACT FROM AUTHOR]

• The loss mechanism of K 2 CO 3 during the deep reduction of oxygen carrier by char. • The occurrences mode of potassium in char and oxygen carrier residues. • K content variations and distributions in char and oxygen carrier residues. • The transformation of K 2 CO 3 to K-Fe-O composites could avoid the loss of K 2 CO 3. Coal-direct chemical looping hydrogen generation (CLHG) is an innovative technology for high-purity hydrogen production and in situ CO 2 capture. The rate-limiting process of the technology is the deep reduction of OC by char, and the addition of K 2 CO 3 to the OC could significantly enhance the reaction rate. Unfortunately, the transformation and migration of K in the reaction may cause the loss of K 2 CO 3. In this work, the K content variations and distributions in the reduction process were investigated in a fixed-bed reactor at 900 °C. The K species in char and OC residues were determined. The results show that K loaded on OC could migrate to the char, and with the reaction prolonged the K in char residues could partially transfer back. After the reduction process, the K in OC and char residues, and the volatile K were 90%, 5.2% and 4.8%, respectively. The possible K species migrating between OC and char were K 2 CO 3. K 2 CO 3 in OC could transform to K-Fe-O composites, which could avoid the K 2 CO 3 loss. The possible K-Fe-O composites were K 2 Fe 22 O 34 , K 2 Fe 10 O 16 in the initial stage and transformed to KFeO 2 finally. A small part of KFeO 2 could be regenerated to K 2 CO 3 by char. The K species in char residues were in the form of K-aluminosilicates, K 2 CO 3 and organic-K during the reduction process. After the reduction process, about 3.5% of K in char residues was water-soluble and could be recovered. 1.7% of K was water-insoluble and difficult to be regenerated. [ABSTRACT FROM AUTHOR]