Currently, production methods of syngas (H2 and CO) generation have attracted much attention. At present, industrial production of syngas is mostly from the conversion of fossil fuels,(1) such as coal gasification,(2,3) methane re-forming,(4) and partial oxidation of methane,(5,6) etc. However, in consideration of the nonrenewable nature of fossil fuels and the environmental impact caused by greenhouse gases, it is a global interest to find renewable and clean energy sources as alternatives to fossil fuels. Abundant worldwide biomass can be obtained from various cheap and nonfood resources,(7,8) such as energy crops, agricultural residues, and organic wastes, etc. Therefore, thermochemical conversion technology for biomass,(9,10) e.g., gasification and pyrolysis, has been considered as a sustainable method for syngas production because of the inexpensive and renewable nature of the raw material. Among various biomass thermochemical conversion technologies, a two-stage pyrolysis–re-forming system(11) has been used to convert biomass to syngas, which possesses unique advantages. The biomass is first rapidly pyrolyzed in the first stage, and the derived vapors, excluding the biochar (retained in the first stage), is catalytically re-formed in the second stage. The biomass is not mixed with the catalyst, which can significantly reduce the carbon deposition on the catalyst surface and improve its re-forming performance.

A stable and efficient catalyst has a significant impact on gasification and pyrolysis.(12,13) Among various catalysts, nickel-based catalysts supported on alumina have been typically used because of the high catalytic performance and low cost. Much research has focused on the modification of nickel-based alumina(14) through the cooperation of transition metal,(15) alkaline earth metal,(16) and alkali metal(17) in order to achieve stable catalysts which can resist coking and sintering effectively...

...The effect of the spinel structure on the catalytic performance of nickel-based alumina has now been thoroughly investigated in this study. Four nickel-based alumina catalysts were prepared using the co-precipitation method and calcined at different temperatures. The catalytic performance of obtained spinel catalysts was investigated for the re-forming of simulated pyrolysis gas (CH4 + CO2) and then applied to the re-forming of gaseous products from rice husks pyrolysis. In addition, various characterization methods were applied to illustrate the textural properties and surface characteristic parameters of catalysts so as to reveal the nature of the influence of spinel structure on the catalytic performance of biomass thermochemical conversion...

Figure 1. TEM images of four fresh catalysts

Figure 2. XRD analysis of fresh catalysts (NiAl2O4, JCPDS No. 78-1601; NiO, JCPDS No. 44-1159; Al2O3, JCPDS No. 10-0425)

Figure 3. H2-TPR of four fresh catalysts.

The results are presented in Figure 3. In some research,(19) the nickel species were divided into three types depending on the different reduction temperatures, the free NiO, the “surface NiAl2O4”, and the crystalline spinel NiAl2O4. Other research(21,22) also reported the same phenomenon in nickel-based alumina and named the reducible Ni2+ species with ?, ?, and ?. However, it should be noticed that there is also a reduction peak of nickel species in their results when the temperature is less than 300 °C, which they both neglected. So we make a change to the way the nickel species divided. The nickel species in the prepared catalysts could be divided into four types in Figure 3, whereas the NiO species with a reduction temperature below 350 °C corresponded to the free NiO, the NiO-Al2O3 species with a reduction temperature at 350–600 °C corresponded to the NiO just supported on Al2O3, the bulk NiAl2O4 species with reducibility at moderate temperatures (600–750 °C) were identified as Ni2+ ions that are not completely integrated into the spinel, and the spinel NiAl2O4 species with a reduction temperature over 750 °C corresponded to the NiO in the spinel structure. In addition, no reduction peaks of alumina support were observed in this reduction temperature range.(21)

Figure 4. Pore size distribution and N2 adsorption–desorption isotherms of the fresh catalysts (solid symbols, adsorption; open symbols, desorption).

Figure 5. Catalytic performance of four catalysts reduced at the temperature of H2-TPR results: a, CH4 conversion ratio; b, ratio of H2/CO; c, H2 selectivity (catalyst dosage, 0.25 g; CO2, 50 mL/min; CH4, 50 mL/min; N2, 100 mL/min; GHSV, 48000 mL/(min/g); re-forming temperature, 650 and 750 °C).

Figure 6. Schematic of the three-dimensional structure of spinel NiAl2O4 catalyst (a), schematic of the surface of spinel NiAl2O4 catalyst (b), and reaction mechanism (c).

Figure 8. Gas composition from pyrolysis–re-forming of biomass (rice husk, 1 g; catalyst dosage, 0.25 g; N2 flow rate, 100 mL/min; water, 4 mL/h; pyrolysis temperature, 600 °C; re-forming temperature, 800 °C).

In this work, the relationship between textural properties of spinel in nickel-based alumina and the catalytic performance has been illustrated in two reaction systems of simulated pyrolysis gas (CH4 + CO2) and real re-forming of gaseous products from rice husks pyrolysis with four kinds of nickel-based alumina catalysts. It is indicated that the spinel structure could improve the catalytic performance and the anticoking property of the catalysts. In the actual re-forming of gaseous products from rice husks pyrolysis, the spinel structure catalysts showed better hydrocarbon conversion performance and higher syngas yield. Various characterization results combined with mechanism analysis proved that, among various structural parameters, the spinel structure could improve the surface microporous properties and increase the pore size of the catalyst, which is closely related to the catalytic performance. When a spinel structure is formed in the catalyst, the nickel species will change the existing form, which also has a significant impact on the performance of the catalyst. Generally, the catalyst with spinel has a better catalytic performance and ability of anticoking.

Organic carbamates are widely used as environmentally benign compounds and unique intermediates of versatile chemical products, including herbicides, pesticides, biologically active compounds, and various kinds of pharmaceutical agents.1?4 Additionally, carbamates play great roles as linkers in organic chemistry and amino groups’ protectors in peptide chemistry. 5,6 Dicarbamates can be decomposed into diisocyanates used in polyurethane production.7,8 This way eliminates hazards of the phosgene-based synthesis of diisocyanates. Moreover, dicarbamates can be directly used to prepare polyurethanes.9,10 Therefore, they may serve as isocyanate-free reagents for polyurethane preparation.

Up to now, several methods to obtain dicarbamates were reported. For example, oxidative carbonylation of diamines,11 the reaction of diamines with dimethylcarbonate (DMC)12?18 or carbamates,19?21 of diamines with urea and alcohol,22?25 of polyureas with dialkylcarbonates,26 of aniline with DMC and subsequent condensation using formaldehyde.27,28

CO2 is a recyclable and naturally plentiful carbon source for various chemical feedstocks and the emissions of CO2 have significantly increased and contributed to global warming.29?31 Thus, the utilization of CO2 has attracted attention in the last decades.32?34

Figure 1. TEM images of (a) commercial CeO2 nanospheres, (b) CeO2(c), and (c) CeO2nanorods.

Figure 2. (a,b) HRTEM images and (c) SAED pattern of CeO2 nanorods.

Figure 3. XRD patterns of commercial CeO2 nanospheres, CeO2(c), and CeO2 nanorods.

Scheme 1. Side Reactions Leading to the Formation of PU and DMC

Figure 4. Product composition vs reaction time for the reaction CO2 + CH3OH + HDA over the CeO2 nanorods catalyst. Reaction conditions: NMP 20 mL, HDA:CH3OH = 5 mmol:500 mmol, CeO2 nanorods catalyst 0.20 g, CO2 5.0 MPa, 423 K.

Figure 5. Logarithmic plot for the influence of CO2 pressure on HDC average formation rate. Reaction conditions: NMP 20 mL, HDA:CH3OH = 5 mmol:500 mmol, CeO2nanorods catalyst 0.20 g, 423 K, 2 h.

Figure 6. (a,b) HRTEM images and (c) SAED pattern of the third regenerated CeO2 nanorods catalyst. The scales for (a) and (b) are 20 and 5 nm, respectively

Catalytic Performance Measurement. The catalytic reaction of HDC formation from CO2, methanol, and HDA was conducted in a 50 mL autoclave with high speed mechanical stirring. Typically, 0.20 g catalyst, 500 mmol methanol, 5 mmol HDA, and 20 mL NMP were put into the autoclave. CO2 was purged into the reactor and released from it for several times to ensure oxygen-free reaction environment. Reactor temperature and the initial pressure of CO2 were set to predetermined values and the reactions were carried out for selected durations. The resultant reaction mixtures were filtered through PES membrane (pore size 0.45 ?m). HDA conversion and HDC productivity were calculated from the results of gas chromatography (Tianmei GC-7900II chromatograph equipped with a flame ionization detector and TM-Wax column) and high-performance liquid chromatography (Shimadzu SPD-M20A HPLC equipped with UV?vis detector and Shimadzu RP C18 (250 mm × 4.6 mm, 5 ?m) column), respectively.

In conclusion, an effective way for the one-pot synthesis of dimethyl hexane-1,6-diyldicarbamate from CO2, methanol, and 1,6-hexanediamine over the CeO2 nanorods catalyst was developed. Under the optimized reaction conditions, dimethyl hexane-1,6-diyldicarbamate was successfully synthesized with around 80% isolated yields. The CeO2 nanorods catalyst can be reused for several runs with slight deactivation. The studies on the influence of different reagents on reaction outcome imply that DMC might be an intermediate in HDC formation and PU alcoholysis is not the main reaction route. This work is the first example of one-pot dicarbamate synthesis from CO2, alcohol, and diamine, being cheap and easily available reagents.

“The brainiest man in baseball”

That was the moniker bestowed upon major league baseball player Morris “Moe” Berg. An alum of Princeton University, NYU, and the Sorbonne, he was fluent in seven languages and had a propensity for reading ten newspapers a day. While this mediocre, third-string catcher’s command of language, foreign affairs, and other esoteric subjects certainly endeared him to the public, they also made him an ideal candidate for a pursuit known to few at the time — his double life as a spy for the OSS.

Plain Language Summary Recent efforts to quantify fugitive methane associated with the oil and gas sector, with a particular focus on production, have resulted in significant revisions upward of emission estimates. In comparison, however, there has been limited focus on urban methane emissions. Given the volume of gas distributed and used in cities, urban losses can impact national‐level emissions. In this study we use aircraft observations of methane, carbon dioxide, carbon monoxide, and ethane to determine characteristic correlation slopes, enabling quantification of urban methane emissions and attribution to natural gas. We sample nearly 12% of the U.S. population and 4 of the 10 most populous cities, focusing on older, leak‐prone urban centers. Emission estimates are more than twice the total in the U.S. EPA inventory for these regions and are predominantly attributed to fugitive natural gas losses. Current estimates for methane emissions from the natural gas supply chain appear to require revision upward, in
part possibly by including end‐use emissions, to account for these urban losses.

Figure 1

(a) Flight coverage by the ECO campaign around the major urban regions of Washington, DC (DC); Baltimore, MD (BLT); Philadelphia, PA (PHL); New York, NY (NYC); Providence, RI (PVD); and Boston, MA (BOS). Each flight is represented by a different color. The inset shows the flight path (black) and the region representing the downwind plume (red) for NYC on 9 May 2018. Map source: Google Maps, Accessed: 18 September 2018 (b) The tracer concentration time series of the NYC plume corresponding to the inset of (a).

Anthropogenic emissions of CH4 from (a) EDGAR v4.2FT2010, (b) gridded EPA, emissions of CO from (c) EDGAR v4.3.2, and emissions of CO2 from (d) EDGAR v4.3.2. EDGAR = Emission Database for Global Atmospheric Research.

Figure 3

Observed correlation slopes (a) CH4:CO2 and (b) CH4:CO, shown in red, compared to the corresponding inventory‐derived ratios for each city. The inventory tracer:tracer values are labeled with the corresponding CH4 inventory used in the analysis (EDGAR v4.2FT2010 [2010, blue], EDGAR v4.3.2 [April 2010, green], and Gridded EPA [2012, orange]), while the average of the five CO2 inventories is used to generate a single CH4:CO2 inventory estimate. Error bars represent 95% confidence intervals determined using the bootstrap methodology detailed in SI Text S5. EDGAR = Emission Database for Global Atmospheric Research.

Figure 4

(a) Methane emissions (kg/s) for the six urban regions calculated by using CH4:CO2 and CH4:CO analyses and (b) summed total emissions (Tg/year) for the five largest cities (Providence excluded) compared to Gridded EPA inventory. Uncertainty on the emission estimates is determined using a bootstrap analysis of the observed slopes and inventories to calculate 95% confidence intervals. For the NG emission estimates in (b), the uncertainty in C2H6:CH4 slope and pipeline C2H6:CH4 is also considered in the boo