Inhibition effect of H2 on char gasification during chemical looping gasification of biomass

Chemical looping gasification (CLG) of biomass produces high contents of syngas, which would have inhibition effect on the gasification of its biomass char. Experiments using a rice husk char as fuel and a low-cost red mud as oxygen carrier for CLG investigation were performed, and effects of temperature, concentrations of steam and H2 on gasification rate were evaluated. Meanwhile, the mathematical models coupling with reaction and diffusion were established focusing on the H2 inhibition on syngas distributions inside and surrounding a single char particle. The results indicated that H2 in the reaction atmosphere has an inhibition effect on its char conversion, and at a high temperature the inhibition effect tends to be stronger. The shrinking core model (spherical symmetry) was found to be suitable to describe the char conversion under the present conditions with the reaction kinetic parameters of E = 128.8 kJ mol−1 and A = 451.2 s−1. In the internal diffusion of a single char particle, the concentrations of CO and H2 both decrease with the increase of dimensionless radius due to the consumption of carbon. In the external diffusion of the char particle, the concentrations of CO and H2 decrease with the increase of the dimensionless radius. The accumulation of H2 inside the char particle prevents CO production, thus inhibiting char gasification

The unique carrier mobility of monolayer Janus MoSSe nanoribbons: a first-principles study.

Charge-carrier mobility is a determining factor of the transport properties of semiconductor materials and is strongly related to the optoelectronic performance of nanoscale devices. Here, we investigate the electronic properties and charge carrier mobility of monolayer Janus MoSSe nanoribbons by means of first-principles simulations coupled with deformation potential theory. These simulations indicate that zigzag nanoribbons are metallic. Conversely, armchair nanoribbons are semiconducting and show oscillations in the calculated band gap as a function of edge-width according to the 3p < 3p + 1 < 3p + 2 rule, with p being the integer number of repeat units along the non-periodic direction of the nanoribbon. Although the charge-carrier mobility of armchair nanoribbons oscillates with the edge-width, its magnitude is comparable to its two-dimensional sheet counterpart. A robust room-temperature carrier mobility is calculated for 3.5 nm armchair nanoribbons with values ranging from 50 cm2 V-1 s-1 to 250 cm2 V-1 s-1 for electrons (e) and holes (h), respectively. A comparison of these values with the results for periodic flat sheet (e: 73.8 cm2 V-1 s-1; h: 157.2 cm2 V-1 s-1) reveals enhanced (suppressed) hole (electron) mobility in the Janus MoSSe nanoribbons. This is in contrast to what was previously found for MoS2 nanoribbons, namely larger mobility for electrons in comparison with holes. These differences are rationalized on the basis of the different structures, edge electronic states and deformation potentials present in the MoSSe nanoribbons. The present results provide the guidelines for the structural and electronic engineering of MoSSe nanoribbon edges towards tailored electron transport properties