Doping B2O3 to Cu/SiO2 catalyst significantly improved activity and long-term performance for glycerol hydrogenolysis to 1,2-propanediol. The strong correlation between 1,2-propanediol yield and Cu ...surface area gave direct evidence that Cu surface area was a key parameter for developing fundamental mechanistic insight into the performance of glycerol hydrogenolysis over Cu-based catalyst.
•B2O3 can promote the dispersion of copper species and stabilize copper particles.•Addition of B2O3 to Cu/SiO2 greatly enhanced activity and stability.•100% Conversion and 98.0% 1,2-propanediol selectivity were achieved over 3CuB/SiO2.•1,2-Propanediol yield was proportional to Cu specific surface area.•Glycerol hydrogenolysis is a structure-sensitive reaction.
Cu/SiO2 catalyst has been extensively applied in glycerol hydrogenolysis for its high selectivity to 1,2-propanediol, while suffering from severe deactivation easily. B2O3 is frequently used as an additive for stabilizing active species. Thus, a series of Cu/SiO2 catalysts with various B2O3 loadings for glycerol hydrogenolysis were prepared via precipitation-gel method followed by impregnation with boric acid. These catalysts were fully characterized by ICP, BET, XRD (in situ XRD), N2O chemisorption, H2-TPR, NH3-TPD, IR, Raman, XPS, and TEM. Addition of B2O3 to Cu/SiO2 can greatly restrain the growth of copper particles and promote the dispersion of copper species upon calcination, reduction and reaction, which resulted in the enhanced catalytic activity and stability. The optimal 3CuB/SiO2 reached complete conversion with 98.0% 1,2-propanediol selectivity. The strong correlation between 1,2-propanediol yield and Cu surface area gave direct evidence that the active Cu species were the primary active sites for glycerol hydrogenolysis.
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•Cr-free Cu-catalysts were investigated for the highly efficient conversion of furfural.•The high yield of 2-methylfuran was attributed to synergistic effect of metal and the weak ...acid sites.•Interactions of copper-support significantly influence the catalytic performance.•The acidic property of Cu-catalysts was closely related to products selectivity in furfural hydrogenation.
Our work focuses on exploring Cr-free Cu-catalysts for the highly efficient conversion of biomass-derived furfural to value-added bio-fuel 2-methylfuran. Three supported Cu-catalysts (Cu/SiO2, Cu/Al2O3, and Cu/ZnO) were prepared by the typical precipitation method, and Cu/SiO2 catalyst exhibited the best catalytic performance with an 89.5% yield to 2-MF. A series of characteristic results indicated that the high yield of 2-methylfuran on Cu/SiO2 catalyst was assigned to synergistic effect of metal and the weak acid sites. Among them, Cu/ZnO catalyst exhibited maximum furfuryl alcohol selectivity because of the large Cu particles, while Cu/Al2O3 catalyst had low 2-methylfuran selectivity due to the insufficient weak acid sites. For Cu/SiO2 catalyst, the highly dispersed Cu particles and the strong metal-support interaction are propitious to its superior catalytic activity. Therefore, copper species are composed on different supports as a result of the different interaction of metal-support to affect their catalytic activity, while products selectivity is related to the acidic property of catalyst. In addition, temperature programmed desorption of furfural indicated that the adsorption–desorption properties of catalyst surface species would influence the rate of furfural hydrogenation.
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•Preparation methods of graphene-like materials from biomass were summarized.•The mechanisms and product characteristics of different methods were discussed.•Common characterization ...instruments to determine the structure were discussed.•Tailored designs of graphene-like material need further investigation.
Two-dimensional graphene materials attracted much attention worldwide because of their superior performance in electronic devices, sensors, and energy storage. However, its application is limited by high cost and insufficient production. The work to find out a simple and environmentally friendly process is highly needed. Designed pyrolysis of biomass precursors can derive graphene-like materials. This review summarizes some typical preparation processes for graphene-like materials synthesis from biomass carbonization via pyrolysis, including salt-based activation, chemical blowing, template-based confinement, coupling with hydrothermal carbonization pretreatment, post exfoliation, and some other methods. The operation of these methods and the performance of obtained graphene-like materials were closely highlighted. The scalability of the techniques and the applications of the biomass graphene-like carbon were also discussed. Some advanced characterization methods, such as SEM, TEM, AFM, Raman, and XPS to determine the graphene-like structure and graphitization degree were also discussed. In the end, some current challenges and future perspectives of the synthesis of these graphene-like materials were concluded.
5-Hydroxymethylfurfural (HMF) is a platform chemical derived from C6 sugars, which can be transformed into various important chemicals and fuels because of the presence of C&z.dbd;O, C-O and furan ...ring functional groups. In this review, the selective tailoring of these groups in HMF to form 2,5-dimethylfuran, 2,5-dihydromethylfuran, 2,5-dihydromethyltetrahydrofuran, 5-ethoxymethylfurfural, 1,6-hexanediol, long-chain alkanes, 3-(hydroxy-methyl)cyclopentanone,
p
-xylene, 2,5-diformylfuran, 2,5-furandicarboxylic acid and maleic anhydride will be described to gain more insight into the transformation of HMF under various conditions. The focus of this review is on the mechanisms of the catalytic processes and potential design strategies for future catalysts. The activation of the functional groups and the key challenges involved in the precise design of bifunctional catalysts are highlighted. Some examples of "one-pot" transformations of fructose into various chemicals using the HMF platform are also presented.
The catalytic mechanisms and catalyst design strategies for 5-hydroxymethylfural conversion are summarized.
•Copper-support interactions significantly influence the hydrogenation activity.•Nature of supports influences selectivity in dimethyl oxalate hydrogenation.•Selective synthesis of ethylene glycol or ...ethanol via tuning solvent and support.•A possible reaction route of dimethyl oxalate hydrogenation was proposed.
The catalytic performances of co-precipitated copper catalysts supported on SiO2, ZrO2 and Al2O3 for dimethyl oxalate hydrogenation were studied. Systematic characterizations showed that copper species formed on different supports as a result of different metal-support interactions influenced the activity and stability, while the nature of supports was closely related to the products distribution in dimethyl oxalate hydrogenation. Mainly large Cu particles were detected over Cu/SiO2 catalyst which exhibited a low activity and stability. For the Cu/ZrO2 catalyst, the highly dispersed Cu particles and the strong metal-support interaction are in favor of its superior activity and stability. Among the catalysts, Cu/SiO2 exhibited maximum ethylene glycol selectivity while Cu/Al2O3 showed a 2-methoxyethanol selectivity of 53.5% in methanol solvent. As tuning the solvent into 1,4-dioxane, an ethanol yield up to 95.5% was received in Cu/Al2O3. The significant difference of selectivity is mainly due to the acidity of the catalysts. Thus, the highly selective synthesis of ethylene glycol and ethanol could be realized by regulating the supports and solvents, and a proper reaction route was proposed.
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► H4SiW12O40/ZrO2 is an effective catalyst for glycerol esterification. ► A 93.6% combined selectivity of glyceryl diacetate and triacetate is achieved. ► H4SiW12O40/ZrO2 can be ...reused up to four consecutive runs without deactivation. ► H4SiW12O40/ZrO2 can be resistant to the impurities present in bulk glycerol.
The synthesis of bioadditives for biofuels from glycerol esterification with acetic acid was performed over zirconia supported heteropolyacids catalysts using H4SiW12O40 (HSiW), H3PW12O40 (HPW) and H3PMo12O40 (HPMo) as active compounds. The as-prepared catalysts were characterized by N2-physisorption, XRD, Raman spectroscopy, NH3-TPD, FTIR of pyridine adsorption and H2O-TPD. Among the catalysts tested, HSiW/ZrO2 achieved the best catalytic performance owing to the better combination of surface Brønsted acid sites and hydrothermal stability. A 93.6% combined selectivity of glyceryl diacetate and glyceryl triacetate with complete glycerol conversion was obtained at 120°C and 4h of reaction time in the presence of HSiW/ZrO2. This catalyst also presented consistent activity for four consecutive reaction cycles, while HPW/ZrO2 and HPMo/ZrO2 exhibited distinct deactivation after reusability tests. In addition, HSiW/ZrO2 can be resistant to the impurities present in bulk glycerol.
Ethanol synthesis from syngas via dimethyl oxalate (DMO) hydrogenation is of crucial importance for environment- and energy-related applications. Herein, we designed the bifunctional Cu nanoparticle ...(NP) inlaid mesoporous Al2O3 catalyst and first applied it to ethanol synthesis with high efficiency. The catalyst was made based on the spatial restriction strategy by pinning the Cu NPs on mesoporous Al2O3 to conquer the sintering problem and facilitate the stability (>200 h at 270 °C), which has potential values in high-temperature and exothermic reactions. The plentiful pores, highly exposed and properly assembled Cu-acid sites, furnished the catalyst with high ethanol yield (∼94.9%). A structure-sensitive behavior that the intrinsic activity increases with the decreasing NP size was discussed. It was attributed to the change in metal–acid interfacial sites, morphology, and electronic structure and balance of surface Cu0–Cu+ species. The mechanism for DMO hydrogenation to ethanol involving activation of CO, C–O, and O–H bands was also proposed. As cleavage of these bonds is a versatile tool to utilize bioderived molecules (e.g., polyols), the bifunctional catalysts can also be applied to hydrogenolysis of C–O bonds or etherification of O–H groups to produce various chemicals.
Abstract
Molecular interactions with both oxides and metals are essential for heterogenous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Here, we show that the ...direct link between the two phases (and not merely being together) is required to selectively hydrogenate CO
2
to methanol on catalysts containing Cu and ZrO
2
. Materials consisting of isolated Cu particles or atomically dispersed Cu–O–Zr sites only catalyze the reverse water-gas shift reaction. In contrast, a metal organic framework structure (UiO-66) with Cu nanoparticles occupying missing-linker defects maximizes the fraction of metallic Cu interfaced to ZrO
2
nodes leading to a material with high adsorption capacity for CO
2
and high activity and selectivity for low-temperature methanol synthesis.
Accelerating write by exploiting PCM asymmetries Jianhui Yue; Yifeng Zhu
2013 IEEE 19th International Symposium on High Performance Computer Architecture (HPCA),
2013-Feb.
Conference Proceeding
Odprti dostop
To improve the write performance of PCM, this paper proposes a new write scheme, called two-stage-write, which leverages the speed and power difference between writing a zero bit and writing a one ...bit. Writing a one takes longer time but less electrical current than writing a zero. We propose to divide a write into stages: in the write-0 stage all zeros are written at an accelerated speed, and in the write-1 stage stage, all ones are written with increased parallelism, without violating power constraints. We also present a new coding scheme to improve the speed of the write-1 stage by further increasing the number of bits that can be written to PCM in parallel. Based on simulation experiments of a multi-core processor under various SPEC CPU 2006 workloads, our proposed techniques can reduce the memory latency of standard PCM by 68.3% and improve the system performance by 33.9% on average. In addition, the proposed two-stage-write shows 16.5% latency reduction and 9.2% performance improvement over Flip-N-Write.
Single-atom catalysts are often reported to have catalytic properties that surpass those of nanoparticles, while a direct comparison of sites common and different for both is lacking. Here we show ...that single atoms of Pt-group metals embedded into the surface of Fe3O4 have a greatly enhanced interaction strength with CO2 compared with the Fe3O4 surface. The strong CO2 adsorption on single Rh atoms and corresponding low activation energies lead to 2 orders of magnitude higher conversion rates of CO2 compared to Rh nanoparticles. This high activity of single atoms stems from the partially oxidic state imposed by their coordination to the support. Fe3O4-supported Rh nanoparticles follow the behavior of single atoms for CO2 interaction and reduction, which is attributed to the dominating role of partially oxidic sites at the Fe3O4–Rh interface. Thus, we show a likely common catalytic chemistry for two kinds of materials thought to be different, and we show that single atoms of Pt-group metals on Fe3O4 are especially successful materials for catalyzed reactions that depend primarily upon sites with the metal–O–Fe environment.
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