Insight into Hydrogenation Selectivity of the Electrocatalytic Nitrate-to-Ammonia Reduction Reaction via Enhancing the Proton Transport

The electrocatalytic nitrate-to-ammonia reduction reaction route (NARR) is one of the emerging routes toward green ammonia synthesis, and its conversion efficiency is controlled mainly by the hydrogenation selectivity. This study proposed a likely NARR route feasible and effective even in a neutral condition. Its high catalytic selectivity and efficiency were achieved by a switch of the sulfate solution to the phosphate buffer solution (PBS), while conditions of NO3- concentration, pH, and applied potential were maintained unchanged. Specifically, the faradaic efficiencies toward NH3 (FENH3) in Na2SO4 were as low as 9.8, 19.8, and 11.4 % versus remarkably jumping to 82.8, 90.5, and 89.5 % in PBS under -0.75, -1.0, and -1.25 V, respectively. The corresponding faradaic efficiencies toward NO2- (FENO2-), 77.0, 69.2, and 73.7 % in Na2SO4, significantly dropped to10.8, 7.4, and 4.4 % in PBS, evidencing an unexpected selectivity reversal of the nitrate reduction from NO2- to NH3. This insight was further revealed by the visualization of the pH gradient near the electrode surface during NARR and confirmed by density functional theory calculations; PBS notably facilitated the proton transport and active mitigation over the proton transfer barrier. The use of PBS resulted in a maximal partial current density toward NH3 (J(NH3)) and NH3 formation rate (r(NH3)) up to 133.5 mA cm(-2) and 1.74 x 10(-7) mol s(-1) cm(-2) in 1.0 m KNO3 at -1.25 V

Lignin-First Monomers to Catechol: Rational Cleavage of C-O and C-C Bonds over Zeolites

A catalytic route is developed to synthesize bio-renewable catechol from softwood-derived lignin-first monomers. This process concept consists of two steps: 1) O-demethylation of 4-n-propylguaiacol (4-PG) over acidic beta zeolites in hot pressurized liquid water delivering 4-n-propylcatechol (4-PC); 2) gas-phase C-dealkylation of 4-PC providing catechol and propylene over acidic ZSM-5 zeolites in the presence of water. With large pore sized beta-19 zeolite as catalyst, 4-PC is formed with more than 93 % selectivity at nearly full conversion of 4-PG. The acid-catalyzed C-dealkylation over ZSM-5 zeolite with medium pore size gives a catechol yield of 75 %. Overall, around 70 % catechol yield is obtained from pure 4-PG, or 56 % when starting from crude 4-PG monomers obtained from softwood by lignin-first RCF biorefinery. The selective cleavage of functional groups from biobased platform molecules through a green and sustainable process highlights the potential to shift feedstock from fossil oil to biomass, providing drop ins for the chemicals industry

Construction of metal organic framework-derived hollow-structured mesoporous carbon based lithium hydroxide composites for low-grade thermal energy storage

Benefiting from its remarkable storage capacity and long energy preservation life-span, salt hydrate thermo-chemical energy storage (TCES) materials build a passable bridge between renewable energy and residential heating. To the best of our knowledge, the application of carbon matrix derived from metal organic frameworks (MOFs) in TCES have not been reported so far. Herein, a brand new LiOH TCES composite with salt hydrate uniformly dispersed in an activated hollow carbon (AHC) with a hollow mesoporous structure derived from the hollow zeolite imidazolate framework is prepared and fully characterized. The resulting Li/AHC2 composite is equipped with excellent hydration performance while exhibiting a maximum heat storage capacity of 1757.1 kJ kg-1 with low working temperature owing to the synergistic effect of cavity structure, large surface area and diversified porosity of AHC2. Besides, compared with pure LiOH, the Li/AHC2-50 with significantly enhanced thermal conductivity can still maintain 90.2% of the original heat storage capacity after 15 dehydration-hydration cycles, highlighting its outstanding fatigue resistance and huge heat transfer application potential. This study not only becomes a new dawn for the effective use of available low-temperature heat sources, but may also inspire new thoughts for expanding the implementation territory of carbon materials derived from MOFs

Pyrolysis of long chain hydrocarbon-based plastics via self-exothermic effects: The origin and influential factors of exothermic processes

Converting plastic wastes into value-added products through energy-efficient pyrolysis is essential, and it requires lower pyrolysis temperatures and shorter processing times than that of other processes. An exothermic phenomenon was observed during the process high-pressure polyethylene pyrolysis. It was proven for the first time that the exotherm is caused by a pressure-induced phase transition, in which colossal heat release can be driven by relatively small pressures. A large temperature change (> 100 degrees C) leads to the deep cracking of polyethylene, although the set temperature is far lower than the required temperature for thermal cracking. Importantly, the heat input stops immediately when the set temperature is reached; thus, the external heating time is short. Polyethylene can be completely converted into liquid products in similar to 90 wt% yield and with a small number of gases. The self-exothermic phase transition only occurs within a certain range of material thickness, which is related to the corresponding phase behavior. In the self-exothermic pyrolysis process, with an increase in the thickness of polyethylene, the proportion of low-value olefins in oil products decreases gradually, while alkanes, isoalkanes and aromatics show an increasing trend, making the product composition closer to the fuel standard. This work provides a viable approach for plastic recycling at low pyrolysis temperatures and short external heating times with the help of a self-exothermic phase transition in the absence of a catalyst

Enhanced enzymatic hydrolysis of poplar cellulosic residue fractionated by a magnetic carbon-based solid-acid catalyst in the gamma-valerolactone-water system

The conventional pretreatment method of poplar comprises multiple steps, including different procedures for fractionating hemicellulose and lignin separately. In our study, hemicellulose and lignin were removed simultaneously by a one-step method. In the gamma-valerolactone (GVL)-water environment, the cellulose retention, hemicellulose removal, and lignin removal rates of 84.94%, 89.08%, and 72.28%, respectively, were achieved over a magnetic carbon-based solid acid (MMCSA) catalyst, under best conditions (160 degrees C, 30 min, 2 g of poplar, 2 g of MMCSA, 35 mL of GVL, and 15 mL of water). The pretreatment of fresh poplar in the reused MMCSA-GVL-water environment showed similar fractionation results as the first time. Scanning electron microscopy characterization of the cellulosic residue revealed the presence of noticeable structural fragmentation. Brunauer-Emmett-Teller characterization showed that the total pore volume of the residue was 2.13 times that of the raw material. The above features of the residue confirmed the high enzymatic hydrolysis potential of the pretreated residue. The enzymatic hydrolysis efficiency of the poplar residue was 67% at a cellulase loading of 20 FPU/g cellulose in dry matter, and it increased to 77.02% at 40 FPU/g cellulose in dry matter. Interestingly, the addition of Tween 80 did not improve the enzymatic hydrolysis efficiency at high cellulase loadings (30 and 40 FPU/g cellulose in dry matter) compared to the case at low cellulase loadings. The relative mechanisms were also analyzed. In this study, a one-step pretreatment method comprising the MMCSA-GVL system for the catalytic depolymerization of poplar wood was developed. The system was verified to be very effective for the subsequent enzymatic hydrolysis of the residues

High yield production of levoglucosan via catalytic pyrolysis of cellulose at low temperature

Pyrolytic sugars are fascinating feedstocks for bio-refinery, and it is of high interest to develop renewable catalysts for biomass pyrolysis. In this study, catalytic pyrolysis of cellulose to levoglucosan (LG) in improved yields was achieved with acid-base bifunctional magnetic Zn-Fe-C catalysts. Among tested catalysts, Zn-4@Fe-C-500 could not only increase LG yield by 5.4 times compared with non-catalytic cellulose pyrolysis at 300 C, but also help lower reaction temperature by 200 C due to acid-base site synergistic effect. Furthermore, the LG yield (80.1 wt %) from catalytic cellulose pyrolysis at 300 C was much higher than that commonly conducted at 500 C without catalyst (60.1 wt%). Thermogravimetric and kinetic analysis disclosed LG formation mechanism. Importantly, Zn4@Fe-C500 catalyst was highly recyclable with little deactivation after 5 consecutive cycles. This study exhibited great potential for industrial LG production from cellulose at low temperatures

Improvement of methanol tolerance and catalytic activity of Rhizomucor miehei lipase for one-step synthesis of biodiesel by semi-rational design

Exploiting highly active and methanol-resistant lipase is of great significance for biodiesel production. A semirational directed evolution method combined with N-glycosylation is reported, and all mutants exhibiting higher catalytic activity and methanol tolerance than the wild type (WT). Mutant N267 retained 64% activity after incubation in 50% methanol for 8 h, which was 48% greater than that of WT. The catalytic activity of mutants N267 and N167 was 30- and 71- fold higher than that of WT. Molecular dynamics simulations of N267 showed that the formation of new strong hydrogen bonds between glycan and the protein stabilized the structure of lipase and improved its methanol tolerance. N267 achieved biodiesel yields of 99.33% (colza oil) and 81.70% (waste soybean oil) for 24 h, which was much higher than WT (51.6% for rapeseed oil and 44.73% for wasted soybean oil). The engineered ProRML mutant has high potential for commercial biodiesel production

Numerical study on flow characteristics of hydrate slurry liquid-solid two-phase flow considering the adhesion between particles

The aggregation effect caused by the adhesion between the hydrate particles in pipe significantly affects the flow characteristics of the fluid, which is closely related to the safe transport of slurry in the pipeline. In this work, a two-fluid model considering the inter-particle adhesion is proposed to investigate the hydrate slurry flow; this model extends the kinetic theory of granular flow, and the inter-particle adhesion is specially considered in the solid phase hydrodynamic properties. Moreover, the population balance model is coupled into the basic two-fluid model to describe the variation of particle number and size. It is found that the maximum deviation between the simulated and experimental values is reduced by 25% compared to the traditional model when the proposed model is adopted to simulate hydrate slurry flow. Simulation work is also carried out to quantify the differences in flow characteristics within the pipeline by two-fluid model with or without considering the inter-particle adhesion. The results indicate that the recognizable increase in the mean size of hydrate can be observed under the condition of the particle adhesion effect is taken into account. Additionally, the effects of various inlet boundary conditions on hydrate slurry flow are explored in detail with the help of the improved two-fluid model. The special two-fluid model developed in this work may pave the way for investigating the flow characteristics of liquid-solid fluids with adhesion characteristics