Aqueous-phase reforming of hydroxyacetone solution to bio-based H_(2)over supported Pt catalysts

Aqueous-phase reforming(APR)is an attractive process to produce bio-based hydrogen from waste biomass streams,during which the catalyst stability is often challenged due to the harsh reaction conditions.In this work,three Pt-based catalysts supported on C,AlO(OH),and ZrO_(2)were investigated for the APR of hydroxyacetone solution in afixed bed reactor at 225℃and 35 bar.Among them,the Pt/C catalyst showed the highest turnover frequency for H_(2)production(TOF of 8.9 molH_(2)molPt^(-1)min^(-1))and the longest catalyst stability.Over the AlO(OH)and ZrO_(2)supported Pt catalysts,the side reactions consuming H_(2),formation of coke,and Pt sintering result in a low H_(2)production and the fast catalyst deactivation.The proposed reaction pathways suggest that a promising APR catalyst should reform all oxygenates in the aqueous phase,minimize the hydrogenation of the oxygenates,maximize the WGS reaction,and inhibit the condensation and coking reactions for maximizing the hydrogen yield and a stable catalytic performance.

The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor

Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（0 to 4.04） and relative humidities（＆lt; 3% to80%） using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde（HCHO） were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH3-UC（=CH2）OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NOx level, while lower at high-NOxlevel. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NOx level is that water vapor promotes the production of Umethacrolein nitrate in the reaction of HOCH2 C（CH3）（OO）CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89 × 10 （-18） cm3/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.

Catalytic performance of zinc-supported copper and nickel catalysts in the glycerol hydrogenolysis

Gas-phase catalytic conversion of glycerol to value added chemicals was investigated over zinc-supported copper and nickel catalysts.The addition of aluminum in the support was also investigated in glycerol conversion and the results indicate an increase in the acidity and adsorption capacity for both copper and nickel catalysts.HRTEM and XRD analysis revealed Ni Zn alloy formation in the Ni/ZnO catalyst.The XRD patterns of the prepared Zn Al mixed oxide catalysts show the presence of Gahanite phase(ZnAl2O4).In addition,H2 chemisorption and TPR results suggest a strong metal-support interactions(SMSI)effect between Ni and Zn O particles.Bare supports Zn O and ZnAl(Zn/Al=0.5)were investigated in the glycerol conversion and they did not present activity.Copper supported on ZnO and ZnAl mixed oxide(Zn/Al=0.5)was active towards hydroxyacetone formation.Nickel was active in the hydrogenolysis of glycerol both for C–C and C–O bonds cleavage of glycerol producing CH4.Strong metal-support interactions(SMSI)between Ni and ZnO has a remarkable suppression effect on the methanation activity during the glycerol conversion.

Fabrication of immobilized nickel nanoclusters decorated by CxNy species for cellulose conversion to C2,3 oxygenated compounds:Rational design via typical C-and N-sources

Production of chemicals and fuels from microcrystalline cellulose has inspired scholars’ attention. Deactivation of metallic catalysts including acid leaching and hydrothermal aggregation is still one of the core issues in these systems. To address these problems, we designed and fabricated a series of Ni-W/SiO2 catalysts, which were decorated by CxNy species using C-and N- sources and applied in cellulose conversion to C2,3 oxygenated compounds. The Ni-W/SiO2@CxNy catalysts, underwent complexing and selfassembling process, exhibited special heterojunctions, accompanying strong interactions mainly among Ni phase and CxNy layers. Catalytic results showed that the heterojunctions and outer CxNy layers extensively enhanced productions of hydroxyacetone(HDA) and ethylene glycol(EG) and promoted the hydrothermal stability through prospering in concentration of Lewis pairs from Ni–N—N structure and immobilizing the metallic nanoclusters. 48.25% of EG was yielded under 5.0 MPa H2 pressurized 240 ℃ water for 2.0 h. The Lewis pair further improved the formation of HDA with 20.92% yield. High hydrothermal stability of NiW/SiO2@CxNy catalyst was proved according to the recycling results and trace leaching concentration of Ni and W. This construction of metallic catalysts exploited a new strategy to manufacture extraordinary durability of metallic nanoclusters for cellulose conversion under harsh reaction conditions.

Catalytic conversion of glucose to small polyols over a binary catalyst of vanadium modified beta zeolite and Ru/C

Catalytic conversion of glucose, the most abundant carbohydrate, to chemicals of petroleum origin has great desirability in terms of sustainability and industrial implementation. In this work, we attempted to exploit the vanadium-based catalysts with high retro-aldol condensation(RAC) activity for the synthesis of small polyols from glucose. Vanadium species incorporated or anchored beta zeolites were found to work effectively in synergy with 1 Ru/AC to produce hydroxyacetone(HA) as the major product(34%)in a semi-continuously stirred tank reactor under 5% glucose concentration. Catalyst characterization by UV-vis and Raman spectral analysis revealed vanadium species mainly stayed in the incorporated form(tetrahedral) at 0.5% of loading and in the supported form(octahedral) at higher loadings up to 8%. Pyridine infrared spectra and temperature programmed desorption of NH3 revealed weak Lewis acid sites in dominance. Vanadium species in the catalysts displayed multiple catalytic roles(isomerization and RAC reaction, and synergism with the hydrogenation catalyst) in the synthesis of HA from glucose. Structureactivity correlation pointed out that the catalytic activity of vanadium species is not dependent on it coordination status, nevertheless, the adjacent vanadium atoms could possibly improve the isomerization rate over the RAC rate in favor of high yield of HA. The catalyst system is recyclable to at least five times without any considerable loss in its activity and structural integrity. The results presented here provide a promising route for the sustainable production of HA and polyols from carbohydrates by using a highly selective vanadium catalyst.

Isosteviol-amino Acid Conjugates as Highly Efficient Organocatalysts for the Asymmetric One-pot Three-component Mannich Reactions

Isosteviol-amino acid conjugates were synthesized and used as chiral catalysts for the asymmetric three-component Mannich reaction with hydroxyacetone as donor molecule. Good yields （up to 98%） and excellent stereoselectivities （up to 97 ： 3 dr and 99% ee） were achieved in a short reaction time. In addition, syn- or anti-configurations of a-hydroxy-β-amino carbonyl compounds were obtained as main products with different chiral catalysts.