Improved photo – Hydrogen production by transposon mutant of Rhodobacter capsulatus with reduced pigment

The light shielding effect of photosynthetic bacteria in photo fermentation process, which is caused by high content of pigment, hinders their hydrogen production rates under intense light irradiation. In order to mitigate this effect and improve hydrogen production efficiency, it is necessary to screen mutants that hold less pigment content. In this study, a mini-Tn5 transposon encoded plasmid pRL27 was employed for transposon mutagenesis of Rhodobacter capsulatus SB1003. A mutant named MC1417 showed significant lower light absorbance from 330 nm to 900 nm compared to its parental strain by UV–visible spectra, and its bacteriochlorophyll a content was reduced by 38%. The results showed that its photo fermentative hydrogen production was improved by 50.5% on the basis of BChl a content using acetate and butyrate as carbon source under intense light irradiation, indicating that it is effective on improving hydrogen production by repressing the pigment biosynthesis. DNA sequencing and BLAST in NCBI Genebank showed that the mutation occurred within its pucDE gene.     

Hydrogen production by Escherichia coli growing in different nutrient media with glycerol: Effects of formate,pH, production kinetics and hydrogenases involved

The Escherichia coli BW25113 or MC4100 wild type parental strains growth and H₂ production kinetics was studied in batch cultures of minimal salt medium (MSM) and peptone medium (PM) at pH of 5.5–7.5 upon glycerol (10 g L^?1) fermentation and formate (0.68 g L^?1) supplementation. The role of formate alone or with glycerol on growth and H₂ production via hydrogenases (Hyd) was investigated in double hyaB hybC (lacking large subunits of Hyd 1 and 2), triple hyaB hybC hycE (lacking large subunits of Hyds 1-3) and sole selC (lacking formate dehydrogenase H) mutants during 24 h bacterial growth. H₂ production was delayed and observed after 24 h bacterial wild type strains growth on MSM. Moreover, it reached the maximal values after 72 h growth at the pH 6.5 and pH 7.5. Biomass formation of the mutants used was inhibited ～3.5 fold compared with wild type, and H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol utilization on MSM at pHs of 5.5–7.5. Formate inhibited bacterial growth on MSM with glycerol, but enhanced and recovered H₂ production by hybC mutant at pH 7.5. H₂ evolution was delayed at pH 7.5 in PM, but observed and stimulated at pH 6.5 upon glycerol and formate utilization in hyaB hybC mutant. H₂ production was absent in hyaB hybC hycE and selC mutants upon glycerol, formate alone or with glycerol fermentation at pH 6.5 and pH 7.5; formate supplementation had no effect. The results point out E. coli ability to grow and utilize glycerol in MSM with comparably high H₂ yield: as well as they suggest the key role of Hyd-3 at both pH 6.5 and pH 7.5 and the role of Hyd-2 and Hyd-4 at pH 7.5 in H₂ production by E. coli during glycerol fermentation with formate supplementation. The results obtained are novel and might be useful in H₂ production biotechnology development using different nutrient media and glycerol and formate as feedstock.     

Hydrogen production by biomass gasification in supercritical water with bimetallic Ni-M/γAl2O3 catalysts (M = Cu, Co and Sn)

Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of original biomass and organic compounds for hydrogen production. In this paper, hydrogen production by SCWG of glucose over alumina-supported nickel catalysts modified with Cu, Co and Sn was studied. The bimetallic Ni-M (M = Cu, Co and Sn) catalysts were prepared by a co-impregnation method and tested in an autoclave reactor at 673 K with a feedstock concentration of 9.09 wt.%. XRD, XRF, N₂ adsorption/desorption, SEM and TGA were adopted to investigate the changes of chemical properties between Ni and Ni-M catalysts and the deactivation mechanism of catalysts. According to the experimental results, the hydrogen yield followed this order: Ni-Cu/γAl₂O₃ > Ni/γAl₂O₃ > Ni-Co/γAl₂O₃ > Ni-Sn/γAl₂O₃. The results show that Cu could improve the catalytic activity of Ni catalyst in reforming reaction of methane to produce hydrogen in SCWG. In addition, Cu can mitigate the sintering of alumina detected by SEM. Co was found to be an excellent promoter of Ni-based catalyst in relation to hydrogen selectivity.     

Hydrogen production from dimethyl ether over Cu/γ-Al2O3 catalyst with zeolites and its effects in the lean NOx trap performance

The purpose of this study is to investigate the effects of mixing three kinds of zeolites (MFI, MOR, and BEA) with the dimethyl ether steam reforming(DME-SR) Cu/γ-Al₂O₃ catalyst to improve H₂ yield at low temperatures, and to identify the de-NOx performance of a combined system of SR catalyst and Lean NOx Trap(LNT). The SR catalyst was prepared by the impregnation method, and a commercialized LNT catalyst was used. The SR reaction experiment was conducted to investigate the effect of the coexistence of CO₂, O₂, NO, and NO₂ among the exhaust gases of the DME engine on the H₂ yield. The study found that the proper mixing of Cu/γ-Al₂O₃ and zeolite increased the H₂ yield at low temperature improving DME hydrolysis. The variation in the H₂ yield according to the kinds of zeolite in the SR catalyst was due to the characteristics of zeolite. The Cu10/γ-Al₂O₃ catalyst mixed with 10% MOR showed the highest H₂ yield. A combined system of SR and LNT uses the H₂ generated mainly from the Cu-based catalyst using the DME-SR reaction for the LNT. When H₂ generated from the SR (Cu10/γ-Al₂O₃ + MOR10) catalyst was used as the reductant of LNT, the NOx conversion at 350 °C or below was improved up to 15% compared to when DME was used. This demonstrates that H₂ as the reductant of LNT is more beneficial than DME. The H₂ generated from the SR catalyst can be used as the reductant of LNT in an after-treatment system. Meanwhile, the SR catalyst that was mixed with zeolite caused the carbon deposition, but the combined system of SR + LNT caused no carbon deposition because the carbon deposited on the SR catalyst reacted with O₂ during the lean-operating period.     

Hydrogen production by catalytic partial oxidation of coke oven gas in BaCo0.7Fe0.2Nb0.1O3−δ membranes with surface modification

The perovskite-type oxygen separation membranes BaCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) combined with Ce_0.8Re_0.2O_2−δ (Re = Sm, Gd) surface modification layers was investigated for hydrogen production by partial oxidation reforming of coke oven gas (COG). The Ce_0.8Re_0.2O_2−δ materials improve the oxygen permeation flux of the BCFN membrane by 8-31% under the COG atmosphere at 875 °C. The high oxygen permeation flux achieved using the Ce_0.8Gd_0.2O_2−δ surface-coating layer in this work is quite encouraging with a maximum value reaching 21.9 ml min⁻¹ cm⁻² at 900 °C. Characterization of the membrane surfaces by SEM and XRD after 100 h long life test show that the Ce_0.8Gd_0.2O_2−δ surface-coating layer on the permeation side can dramatically withstand corrosion of the hash strong reductive working conditions, which will be promising surface modification material in the catalytic partial oxidation reforming of COG using oxygen-permeable ceramics.     

Enhanced oxygen tolerance of hydrogenase from Klebsiella oxytoca HP1 by Gly–Cys exchanges nearby Fe–S clusters as biocatalysts in biofuel cells or hydrogen production

Hydrogenase is the key point of H₂-based biotechnology. However, the O₂-sensitivity largely hinders its applications in biofuel cells and biological H₂ production. Therefore, substantial breakthrough on understanding the molecular basis of O₂-sensitivity and developing more O₂-tolerant hydrogenases are urgently required. In this study, we found adding extra cysteines to the vicinity of the proximal Fe–S cluster to the NiFe active centre could largely enhance oxygen tolerance of hydrogen-evolving hydrogenase 3 from Klebsiella oxytoca HP1 (KoHyd3), through homologous sequence comparison and site-directed mutagenesis. Ratio of aerobic hydrogen yield to anaerobic hydrogen yield (RHH) of Gly47Cys (Gly47 was replaced with Cys47), Gly50Cys, Gly113Cys, Gly120Cys and Gly50Cys–Gly120Cys (double exchange) were increased by 46.99%, 42.15%, 59.19%, 44.74% and 78.72%, respectively, comparing with that of wild type. Moreover, TiO₂-KoHyd3 (Gly47Cys, Gly50Cys, Gly113Cys, Gly120Cys and Gly50Cys–Gly120Cys) particles acted well in UV light-driven H₂ production from water. These results revealed that extra cysteines nearby Fe–S clusters had significant effects on oxygen tolerance of KoHyd3. It also provided a promising way to produce O₂-tolerant hydrogenase as biocatalysts in biofuel cells or H₂ production by photolysis of water.     

Hydrogen production by biomass gasification in supercritical water over Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts. The catalytic activity and H₂ selectivity of Ni/CeO₂-γAl₂O₃ was higher than that of Ni/γ-Al₂O₃ catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO₂-γAl₂O₃ catalyst had a certain role in the inhibition of carbon deposition and coking.