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The hydrogenation of methyl formate to methanol is considered one of the most effective methods for recycling methyl formate products. We recently developed a highly efficient and cost-effective Cu-SiO2 catalyst using the ammonia-evaporation (AE) method. The Cu-SiO2-AE catalyst demonstrated superior performance, achieving a methyl formate conversion of 94.2% and a methanol selectivity of 99.9% in the liquid product. The catalyst also displayed excellent stability over a durability test of 250 h. Compared to the commonly used Cu-Cr catalyst in the industry, the Cu-SiO2-AE catalyst exhibited higher conversion of methyl formate and methanol yield under the same reaction conditions. Characterization results revealed a significant presence of Si-OH groups in the Cu-SiO2-AE catalyst. These groups enhanced the hydrogen spillover effect and improved hydrogenation efficiency by preventing sintering during the reaction to stabilize the Cu species. The strategy employed in this study is applicable to the rational design of highly efficient catalysts for industrial applications.

Plasma enhanced atomic layer deposition (PEALD) SiN gate dielectric is performed on AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT). The fabricated MIS-HEMTs with 5 nm SiN gate dielectric layer exhibits a tiny threshold voltage hysteresis (~ 0.04 V), sufficiently decreased leakage current of ~10−9 A/mm at ${V}_{\text {GS}} =-{60}$ V and good threshold voltage ( ${V}_{\text {TH}}$ ) stability even measured at 200 °C. The increased mobility of 2-D electron gas (2-DEG) and suppressed current collapse are demonstrated, thereby producing a power density of 7.05 W/mm with an associated 34.0 % power-added efficiency (PAE) and a peak PAE of 51.4 % in a continuous-wave mode at 30 GHz.

A Ka -band AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (MIS-HEMT) with SiN gate dielectric grown by plasma-enhanced atomic layer deposition (PEALD) is demonstrated. The gate reverse leakage current in a controlled HEMT is reduced by about three orders of magnitude by the PEALD-SiN, contributing to an improved breakdown voltage of 92.5 V (source–drain separation of $2.0~\mu \text{m}$ ) in the fabricated MIS-HEMTs. The MIS-HEMTs also feature small threshold voltage hysteresis in dc transfer and capacitance–voltage characterizations, suggesting a good PEALD-SiN/AlGaN interface. The fabricated MIS-HEMTs deliver a high output power density of 7.16 W/mm and a peak power-added efficiency of 60.3%, respectively, at ${V}_{\text {DS}} =30$ V and ${V}_{\text {DS}} =10$ V in pulse mode at 28 GHz. PEALD-SiN could be a compelling gate dielectric for fabrication of high-power and high-efficiency MIS-HEMTs.

Low damage atomic layer etching (ALE) gate recess is developed for fabrication of millimeter-wave AlGaN/GaN high-electron-mobility transistors (HEMTs). Plasma ion induced bombardments to the AlGaN barrier is effectively suppressed by the ALE recess, contributing to a well-controlled recessed surface morphology. The suppressed lattice damage to AlGaN/GaN heterostructure is also reflected by a significantly reduced gate leakage as well as an invisible threshold voltage shift associated with damage induced traps. With a 0.15- $\mu \text{m}$ T-gate fabrication technology, a high power-gain cutoff frequency ${f}_{\text {MAX}}$ of 205 GHz has been achieved. The ALE-recessed AlGaN/GaN HEMTs exhibits a record high power-added-efficiency (PAE) of 43.6% at 40 GHz in a continuous-wave mode. The associated gain and output power density are also remarkably improved compared with controlled HEMTs with conventional gate recess process.

In this letter, a high-temperature (HT) gate recess technique is implemented into the fabrication of high-performance millimeter-wave AlGaN/GaN high-electron-mobility transistors (HEMTs). By virtue of the low damage feature of the HT recess, a high extrinsic transconductance of 422 mS/mm, a three-terminal breakdown voltage of 134 V with a source–drain separation of 2.4 $\mu \text{m}$ , and a remarkable low Schottky gate leakage current of $1.6\times 10^{-6}$ A/mm at ${V}_{\textsf {GS}} = -\textsf {60}$ V are achieved, which is at least two orders of magnitude lower than the HEMTs with gate recessed at room temperature. By employing a 0.2- $\mu \text{m}$ T-shaped gate technology, a current-gain cutoff frequency ${f}_{T}$ of 81 GHz and a unit-power-gain frequency ${f}_{\textsf {MAX}}$ of 194 GHz are realized. The current collapse in the HT-recessed AlGaN/GaN HEMTs is significantly suppressed, contributing to a record high power-added-efficiency of 42.8%, as well as high output power density of 5.1 W/mm at 35 GHz in a continuous-wave mode.

Superior iron-based Fischer-Tropsch synthesis (FTS) catalysts (Fe/NMCs) were developed by impregnating high amount of iron (40 wt%) over nitrogen-rich mesoporous carbons (NMCs) with high porosities. The large pore volumes and specific surface areas of NMCs realized the high loadings and proper dispersions of iron while the nitrogen-containing groups enhanced the basicities of the catalysts. Weak metal-support interactions were observed in Fe/NMCs, which improved the reduction, carburization of iron, and further the FTS activities. FTS tests indicated a medium amount of nitrogen (≤8.3 wt%) did not show obvious effect on the activity of the catalyst, but a much higher amount of nitrogen (≥16.5 wt%) could result in a significant decrease of activity. Nitrogen-containing groups could effectively suppress the methane selectivity and improve the lower olefins selectivity in the FTS reaction. The hydrocarbon productivity of the Fe/NMCs was up to 0.62 g HC/(h·g cat.) at 260 °C, 1 MPa, and H2/CO ratio of 1, much higher than that of any other iron catalyst reported under similar conditions. As a result of the superior performance, Fe/NMCs could be one of ideal candidates for iron-based FTS catalysts in the future.

Iron-based Fischer-Tropsch synthesis (FTS) has received renewable interests due to the gradual depletion of crude oil resources and its flexible product adjustment from lower olefins to long-chain hydrocarbons. However, one of the main challenges of iron-based FTS catalysts is the relative lower activity or productivity (per gram catalyst) at low or middle temperature. In this work, ultra-active iron-based FTS catalysts (Fe/SMC) were developed by loading iron over spherical mesoporous carbon (SMC) with huge porosity. The large pore volume (2.22 cm 3 /g) and high specific surface area (767 m 2 /g) of SMC allowed the high iron loading (up to 50 wt%) with proper dispersion. Weak C-Fe interaction was observed in the Fe/SMC catalysts, which was favorable for the reduction of iron and its further carburization to form more active sites of FTS. Activity tests showed that the Fe/SMC catalysts exhibited ultra-high activities in FTS. With the increase of iron loadings (30–50 wt%), the FTS rates (FTY, mmol CO/(h·g cat.)) of Fe/SMC catalysts increased due to the larger iron surfaces exposed at higher iron loadings. Small amount of K promoter significantly enhanced the FTY and apparent turnover frequency (TOF, S −1 ) of the Fe/SMC catalysts. The hydrocarbon productivity of K-promoted catalyst (40FeK/SMC) was up to 0.91 g HC/(h·g cat.) (260 °C, H 2 /CO = 1, 2 MPa), much higher than that of any other supported or unsupported iron-based FTS catalysts reported at similar reaction conditions. The results obtained in this work will open a new avenue for the development of highly active iron-based FTS catalysts.

The infiltration process in slopes is an essential issue in geotechnical engineering. A new Green-Ampt model for describing the two-stage infiltration in slopes based on fractional derivatives was proposed in this paper. The Green and Ampt (1911) ’s model, and Chen and Young (2006) ’s model are two special cases of the proposed model. A 1D loess soil column test in the literature as well as a laboratory rainfall test of loess slope were used to validate the proposed model. The travel curve of wetting front obtained by the proposed model was obviously closer to the actual test value than that obtained by the Chen and Young’s model, indicating that the performance of the proposed model is superior to the Chen and Young’s model due to the use of fractional derivatives. The proposed Green-Ampt model was combined with a rigorous 3D limit equilibrium method to obtain the real-time safety factor of the slope during rainfall. The calculated failure time of the loess slope by the proposed method is close to the actual failure time of the laboratory test, while the corresponding of Chen and Young’s model is obviously shorter than the actual status. Six parameters are included in the proposed model, and sensitivity analysis shows that the fractional derivative has the most significant impact on the wetting front depth, followed by the permeability coefficient, moisture content difference, suction head, rainfall intensity, and slope angle.

Mesoporous Ni-Mg-Al and Ni-Al catalysts were facilely synthesized via evaporation-induced self-assembly (EISA) method and employed for coupled reforming reaction consisting of dry reforming of methane (DRM) and partial oxidation of methane (POM) to produce syngas (H 2 + CO). The Ni-Mg-Al and Ni-Al catalysts with encapsulated nickel nanoparticles were directly synthesized in one-pot way. For comparison, Ni/Al 2 O 3 as reference catalyst was also prepared by general impregnation method. Characterization by BET, XRD and H 2 -chemisorption revealed that the Ni-Mg-Al catalyst owned larger surface area and higher Ni dispersion as well as smaller metallic Ni particles size compared to Ni-Al and Ni/Al 2 O 3 catalysts. CO 2 -TPD demonstrated that the Ni-Mg-Al catalyst presented stronger basicity due to Mg incorporation. H 2 -TPR confirmed that the reduction of Ni-based species to Ni 0 was performed in high temperature due to the formed NiAl 2 O 4 phase. Activity tests indicated that this Ni-Mg-Al catalyst, due to its excellent physicochemical property, exhibited higher CH 4 conversion, H 2 selectivity, and H 2 /CO ratio in the coupled DRM-POM reaction. XRD, SEM and TG-DTA analyses of the used catalysts disclosed that the Mg-modified Ni-Mg-Al catalyst for syngas production using coupled DRM-POM reaction exhibited robust resistance to coke deposition. Consequently, by the synergistic cooperation between the coupled DRM-POM reaction and Mg-modified Ni-Mg-Al catalyst, high catalytic activity and stability could be accomplished to produce syngas.

Silicalite-1 zeolite coating was coated on the honeycomb-like monolithic SiC foam via hydrothermal synthesis method. The as-made Silicalite-1-coated SiC (S-1/SiC) was used as catalyst support to prepare a novel supported Ni monolith catalyst (Ni/S-1/SiC) by impregnation method. The Ni/S-1/SiC monolith catalyst was characterized by X-ray diffraction (XRD), N 2 physical adsorption, scanning electron microscope (SEM), thermogravimetry (TG), etc. The analysis results of XRD and SEM disclosed that Silicalite-1 coating successfully grew in situ on the SiC surface under the employed hydrothermal conditions. The Ni/S-1/SiC monolith catalyst was employed for syngas production in a combined reforming reaction consisting of CO 2 dry reforming of methane (CDRM) and partial oxidation of CH 4 (POM). Activity results indicated that the Ni/S-1/SiC monolith catalyst exhibited better catalytic activity than Silicalite-1 supported Ni catalyst (Ni/S-1) and SiC supported Ni (Ni/SiC) catalyst. The Silicalite-1 coating on the Ni/S-1/SiC catalyst combined the SiC support and Ni-based species tightly, leading to the enhanced catalytic performance of Ni/S-1/SiC catalyst. The stability test indicated that the Ni/S-1/SiC monolith catalyst also presented excellent stability and strong resistance to carbon deposition, which was attributed to the high heat conductivity of SiC, the presence of Silicalite-1 being coated on SiC as well as the combined reforming reaction of CDRM-POM. Furthermore, the H 2 /CO molar ratio of syngas generated in the combined CDRM-POM reaction over Ni/S-1/SiC catalyst could be tuned facilely by adjusting the proportion of O 2 coexisting in feed gas.

A silicon carbide (SiC) foam monolith decorated with a carbon nanofibers (CNFs) layer was employed as the catalyst support for Ni-based catalyst preparation, used for the CO2 dry reforming of methane (DRM) reaction. The loading amount of CNFs on the SiC foam monolith was 6.6 wt.%, which obviously increased the surface area of the pristine SiC foam from 4 m2/g to 24 m2/g. The prepared CNFs layer strongly attached to the pristine SiC surface and was considerably stable even after 100 h time on stream (TOS) DRM reaction. The CNFs decorated SiC composite support provided more anchorage sites for improving the dispersion of the Ni particles and enhanced the metal-support interaction compared to the pristine SiC support. Compared with other catalysts such as Ni/SiC and Ni/CNFs, the Ni/CNFs-SiC catalyst exhibited not only the highest activity but also remarkable stability during DRM reaction. The XPS and SEM-EDS results showed that the carbon deposition over the nickel surface of Ni/CNFs-SiC catalyst was much less than those of Ni/SiC and Ni/CNFs catalysts. In addition, the XRD analysis verified that almost no sintering of nickel particle was detected over the Ni/CNFs-SiC catalyst, which was prepared with CNFs-SiC composite as catalyst support, even after 100 h TOS DRM reaction at 750 °C.

The upgrading and reforming of coal-derived liquids are necessary for the application of high value-added liquid fuels, but the processing is difficult due to the amounts of impurities. In this paper, the catalytic cracking of 4-(1-naphthylmethyl)bibenzyl (NMBB) as a model reaction was studied deeply under sub- and supercritical water environment. Water might serve as a cheap and environmental H donor, which was more efficient than the supplied H2 in the processing of coal-derived liquids upgrading. Meanwhile, sub- and supercritical water could provide a homogeneous reaction environment for NMBB cracking as special solvents. The NMBB conversion under subcritical water was much higher than that under supercritical water. Furthermore, for H2 atmosphere, NMBB conversion was higher than that of N2 atmosphere, indicating that the process of in-situ H2 formation from subcritical water was more easily. Therefore, the cracking of NMBB under subcritical water and H2 atmosphere could be regarded as a reasonable reaction condition.

This study focused on the synthesis of hydrocarbon fuel containing a high iso-paraffin and very low oxygen content from palm oil using a mixed acid–base catalyst. The catalysts were characterized by nitrogen adsorption–desorption, X-ray diffraction, hydrogen-temperature programmed reduction, carbon dioxide- and ammonia-temperature programmed desorption as well as thermogravimetric analysis. Solid base (MgO, CaO, SiO2, and Na2SiO3) and solid acid (HY, H-beta, HZSM5, and Al2O3) catalysts were individually evaluated for their catalytic activity in a semi-batch reactor in terms of the deoxygenation level of palm oil product. The best acid and alkali catalyst were then selected for mixing at different weight ratios and re-tested for their tandem catalytic performance in terms of the deoxygenation activity. Finally, the reaction temperature (400–460 °C), pressure in a nitrogen or hydrogen gas atmosphere and residence time were optimized. The main components in the liquid product obtained were normal paraffins, iso-paraffins, olefins and aromatics. For the single base catalysts, a liquid yield of higher than 65 wt% was obtained at a 460 °C using MgO catalyst, which also realized an excellent oxygen removal through decarboxylation and decarbonylation. For the single acid catalysts, the zeolite beta catalysts reached a liquid yield of around 55 wt% with high iso-paraffin content. The optimal MgO:beta zeolite weight ratio for the acid–base hybrid catalyst was 3:1, which resulted in a low oxygen content in the products with a high iso-paraffin (35%) content.

The application of rice-bran catalysts containing “biopromoters”, from rice bran, in the production of synthetic oil was investigated. Trace minerals such as K, Mg, and Mn from rice bran were successfully incorporated into Fe@C microspherical cores and played a cooperative promotional role on the iron species. The yield of the hydrocarbons was strikingly higher than that obtained with the unpromoted catalyst. Further, rice bran is a natural carbon source, not a chemical carbon source, that can be used to fabricate the carbon microsphere support. This concept opens a new avenue for recycling and boosts the value of abundant waste biomass in nature.

In this letter, we report high-performance enhancement-mode (E-mode) Al2O3/AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) fabricated with high-temperature low-damage gate recess technique. The high-temperature gate recess is implemented by increasing the substrate temperature to 180 °C to enhance the desorption of chlorine-based etching residues during the dry etching of AlGaN barrier. High-crystal-quality Al2O3 gate dielectric was grown by atomic-layer deposition using O3 as the oxygen source to suppress hydrogen-induced weak bonds. The fabricated E-mode MIS-HEMTs exhibit a threshold voltage of 1.6 V, a pulsed drive current of 1.13 A/mm, and very low OFF-state standby power of $6.8 \times 10^{\mathrm {-8}}$ W/mm at $V_{\mathrm {GS}} =0$ V and $V_{\mathrm {DS}} =30$ V. At 4 GHz and in pulse-mode operation, the output power density and power-added efficiency were measured to be 5.76 W/mm and 57%, both of which are the highest for GaN-based E-mode MIS-HEMTs reported to date.

PurposeThe purpose of this paper is to report upon high power, internally matched GaN high electron mobility transistors (HEMTs) at Ku band with 1.5 GHz bandwidth, which employ a simple and cost‐effective lossless compensated matching technique.Design/methodology/approachTwo 4 mm gate periphery GaN HEMTs are parallel combined and internally matched with multi‐section reactive impedance transformers at the input and output networks. The output matching network is designed at the upper frequency of the design band for a flat power of the circuit, while the input matching network is designed at the upper frequency for a flat gain.FindingsWith the reactively compensated matching technique, the internally matched GaN HEMTs exhibit a flat saturated output power of 43.2+0.7 dBm and an average power added efficiency of 15 per cent over 12 to 13.5 GHz.Originality/valueThis paper provides useful information for the internally matched GaN HEMTs.

A C-band linear power amplifier is successfully developed with a one-chip 2 mm AlGaN/GaN high electron mobility transistors (HEMTs). Two kinds of matching circuits for the linear power amplifier are compared. Besides, stabilization methods for the amplifier are also discussed. At 5.4 GHz, the developed GaN HEMTs linear power amplifier delivers a 37.2 dBm (5.2 W) cw P1 dB output power with 9 dB linear gain and 55.7% maximum power-added efficiency (PAE) with a drain voltage of 25 V. To our best knowledge, the achieved PAE is the state-of-the-art result ever reported for 2 mm gate width single die GaN-based hybrid microwave integrated power amplifier at C-band.

Cytoplasmic male sterility (CMS) is essential for sunflower hybridproduction. CMS-GIG2, a new sunflower CMS type, was furtherconfirmed by crossing with the maintainer and restorer lines for theCMS-PET1, both of which maintain the male sterility of CMS-GIG2.Meiotic division in CMS-GIG2 was observed with 4¢6-diamidino-2-phenylindole dihydrochloride staining, indicating that microsporeformation was disrupted before the meiotic cytokinesis was com-pleted. Light microscopy observation showed that both middle layerand tapetal cells expand radially rather than degrade over time,followed by failure to form tetrads and normal microspores. Thismorphological defect leading to male sterility in CMS-GIG2 differsfrom that observed in the PET1 CMS type. CMS-GIG2 will certainlyprovide additional genetic diversity for sunflower hybrid breedingprogrammes. Key words: Helianthus annuus L. — cytoplasmic male sterility— microsporogenesis — meiotic divisionCytoplasmic male sterility (CMS) is a maternally inheritedtrait that has been described in more than 150 plant species,and is characterized by the inability to produce functionalpollen grains, but both vegetative and female development areunaffected (Kaul 1988). The FAO Technical Consultation ofthe European Cooperative Research Network on Sunflowerreported 72 male-sterile sunflower sources of different origins(Serieys 2005), including (i) mutants spontaneously occurringin nature, such as ANN1, ANN2, ANN3 and ANN4(Serieys 1984); (ii) interspecific cross progeny such as ARG3(Christov 1992), CMG1, CMG2 and CMG3 (Whelan andDedio 1980); (iii) intraspecific crosses progeny such as ANT1(Vranceanu et al. 1986), ANL2 (Heiser 1982) and ANL1(Anashchenko et al. 1974) and (iv) MUT1 and MUT2 frommutagenesis of two maintainer lines for the PET1 cytoplasm(Christov 1993). SunflowerCMS-PET1wasfirstidentifiedintheprogeny of the interspecific cross Helianthus petiolaris ·Helianthus annuus (Leclercq 1969), which is the only sourceextensively used in oilseed hybrid production. In addition toidentifying new sources of CMS and corresponding fertilityrestorers to broaden the genetic diversity of hybrid seedproduction, more research work has been focused on theabortionmechanismaswellasthechimericgenesrelatedtoCMS.The observation of microsporogenesis development inCMS-PET1, with the cytoplasm of H. petiolaris and nucleusof H. annuus, indicates that the anther abortion is due totapetum degeneration and disintegration after meiosis II(Horner 1977, Laveau et al. 1989). In some crops, such asPennisetum glaucum L., Triticum aestivum L., Brassica napus L.and Zea mays L., different CMS cytoplasm genotypes with thesame nuclear genotype display various abortion stages,abortion process of microspore development or abnormaltapetum (Li and Sun 1996, Chhabra et al. 1997, Zhou et al.1997, Long et al. 2005). Therefore, the observation ofmicrospore development in different sunflower CMS typeswill extend our knowledge of the important cytoplasmic effectsoccurring during pollen production.The objectives of this study were to compare the antherdevelopment of CMS-GIG2 with HA 89, a public oilseedsunflower inbred maintainer line to confirm the abortion stageof the new CMS, meanwhile, we can primarily identify a newCMS type different from PETl (H. petiolaris cytoplasm andH. annuus nucleus) based on its different reflects in themicrospore abortion as well as cross with some identified linesfor PET1.

The effects of interface oxidation on the transport behavior of the 2-D electron gas (2DEG) in AlGaN/GaN heterostructures by plasma-enhanced-atomic-layer-deposited AlN (PEALD-AlN) passivation were investigated using temperature-dependent Hall-effect and X-ray photoelectron spectroscopy (XPS) characterizations. AlGaN/GaN heterostructure with a 4-nm-thick PEALD-AlN passivation exhibits good 2DEG transport behavior and stability at moderately high temperature (e.g., 275 °C). However, serious oxidation of the AlN/GaN (cap layer) interface occurs as the sample is heated up to 400 °C in low-pressure atmosphere, as verified by an increased Ga-O bond in Ga 3d core-level spectra. The oxidation leads to a significant reduction of 2.47 × 1012 cm−2 in the 2DEG density in the channel. A modified AlN passivation structure with Al2O3/AlN (10/4 nm) stack is shown to be able to effectively suppress the oxidation of the AlN/GaN interface, demonstrating an enhanced 2DEG density and high-temperature stability even when the sample is heated up to 500 °C. Based on XPS and 2DEG recovery experiments, it is suggested that acceptor-like deep levels have been generated in the near-surface region of AlGaN/GaN heterostructure because of the oxidation, and trapping of these deep levels results in significant depletion of the 2DEG in the channel. The effects of PEALD-AlN passivation on the strain in the AlGaN barrier of AlGaN/GaN heterostructures are also evaluated with high-resolution X-ray diffraction technique.