Brazilian energy policies side-effects on CO2 emissions reduction

This study focuses on some of the programs and measures Brazil has undertaken over the past two or three decades in order to mitigate economic or environmental problems, which have also had positive effects on the reduction of the country's carbon dioxide emissions. Results show that, in the year 2000 alone, some 11% in CO₂ emissions from energy use in Brazil have been reduced compared to what would have been emitted that year had the actions reviewed here not been implemented in good time. As these actions have not been motivated as a strategy to curb global climate change, if their benefits related to avoided carbon emissions are not fully appraised in the near future, chances are that these policies may be discontinued. For instance, in the case of the business-as-usual scenario drawn up by the Ministry of Mines and Energy in 2001, the discontinuity of the policies analyzed here would result in CO₂ emissions 20% higher by 2020, compared to what would happen were these policies kept over the long term. Therefore, the perspective presented here spotlights some of the hidden benefits of the programs and measures underway in the country, justifying their continuation or even intensification.     

Impact of CO2 reduction policies on the development of renewable energy sources

The paper examines the impact of CO₂ reduction policies on the strategic planning of the energy sector. Attention is paid to the conflicts between economic and environmental goals influencing the penetration of renewable energy sources (RES). A linear programming (LP) model is applied to represent the structure of the Greek energy system. Energy flows are optimized with respect to the system's economic efficiency. The model incorporates a constraint concerning the CO₂ emissions generated from the various energy production and consumption activities. The results show that a substantial reduction of CO₂ emissions can be achieved through a large scale integration of RES into the energy system. Shadow prices identified by the model denote the real cost for the economy of using alternative energy forms under various environmental restrictions. They are useful to indicate the changes in the prevailing pricing mechanisms that are necessary to direct the market forces towards the desired policy goals.     

The impacts of carbon tax and complementary policies on Chinese economy

Under the pressure of global warming, it is imperative for Chinese government to impose effective policy instruments to promote domestic energy saving and carbon emissions reduction. As one of the most important incentive-based policy instruments, carbon tax has sparked a lively controversy in China. This paper explores the impact of carbon tax on Chinese economy, as well as the cushion effects of the complementary policies, by constructing a dynamic recursive general equilibrium model. The model can describe the new equilibrium for each sequential independent period (e.g. one year) after carbon tax and the complementary policies are imposed, and thus describe the long-term impacts of the policies. The simulation results show that carbon tax is an effective policy tool because it can reduce carbon emissions with a little negative impact on economic growth; reducing indirect tax in the meantime of imposing carbon tax will help to reduce the negative impact of the tax on production and competitiveness; in addition, giving households subsidy in the meantime will help to stimulate household consumptions. Therefore, complementary policies used together with carbon tax will help to cushion the negative impacts of carbon tax on the economy. The dynamic CGE analysis shows the impact of carbon tax policy on the GDP is relatively small, but the reduction of carbon emission is relatively large.     

Review of photocatalytic and photo-electrocatalytic reduction of CO2 on carbon supported films

CO₂ capture/conversion is one of the biggest challenges facing humanity. This review reports on the analysis of the research performed over the last five years on the application of carbon-based materials as supports for CO₂ conversion using the photo (electro)catalytic approach. Three types of photocatalyst materials – metals, metal-oxides, non-oxides, and their combinations with carbon are presented. Our focus has been on i) carbon – based structures and their unique features that assist with photocatalysis, ii) the approaches to consider for photo (electro)catalytic CO₂ conversion, iii) representative examples of different carbon allotrope supported composites for CO₂ conversion, and iv) tools to perform quantitative estimation of their performance. We have provided insights into the benefits of reduced graphene oxide (rGO) based on our team's research and listed the areas where not only improvement in CO₂ reduction reactions can be considered but also areas of interest in other applications where rGO can be leveraged in a beneficial manner.     

Implications of uncertainty on regional CO2 mitigation policies for the U.S. onroad sector based on a high-resolution emissions estimate

In this study we present onroad fossil fuel CO₂ emissions estimated by the Vulcan Project, an effort quantifying fossil fuel CO₂ emissions for the U.S. in high spatial and temporal resolution. This high-resolution data, aggregated at the state-level and classified in broad road and vehicle type categories, is compared to a commonly used national-average approach. We find that the use of national averages incurs state-level biases for road groupings that are almost twice as large as for vehicle groupings. The uncertainty for all groups exceeds the bias, and both quantities are positively correlated with total state emissions. States with the largest emissions totals are typically similar to one another in terms of emissions fraction distribution across road and vehicle groups, while smaller-emitting states have a wider range of variation in all groups. Uncertainties in reduction estimates as large as ±60% corresponding to ±0.2 MtC are found for a national-average emissions mitigation strategy focused on a 10% emissions reduction from a single vehicle class, such as passenger gas vehicles or heavy diesel trucks. Recommendations are made for reducing CO₂ emissions uncertainty by addressing its main drivers: VMT and fuel efficiency uncertainty.     

The role of biofuels for transportation in CO2 emission reduction scenarios with global versus regional carbon caps

This study analyzes how international climate regimes affect cost-efficiency of fuel choices in the transportation sector. The analysis is carried out with a regionalized version of the Global Energy Transition model, GET-R 6.0. Two different carbon dioxide (CO₂) reduction scenarios are applied, both meeting an atmospheric CO₂ concentration target of 450 ppm by the year 2100. The first scenario, “global cap” (GC), uses a global cap on CO₂ emissions, and global emissions trading is allowed. In the second scenario, “regional caps” (RC), industrialized regions start to reduce their CO₂ emissions by 2010 while developing regions may wait several decades and emission reductions are not tradable across regions. In this second scenario, CO₂ emissions are assumed to meet an equal per capita distribution of 1.0 tC/capita, in all six regions, by 2040; emissions then follow a common reduction path, toward approximately 0.2 tC/capita by 2100. Three main results emerge from our analysis: (i) the use of biofuels in the industrialized regions is significantly higher in RC than in GC; (ii) the use of biofuels in RC actually increases the weaker (i.e., higher) the CO₂ concentration target (up to 550 ppm); and (iii) biofuels never play a dominant role in the transportation sector. We find that biofuels may play a more important role in industrialized countries if these take on their responsibilities and reduce their emissions before developing countries start reducing their emissions, compared to the case in which all countries take action under a global cap and trade emission reduction regime.     

Covalent hybrid of hemin and mesoporous carbon as a high performance electrocatalyst for oxygen reduction

A high performance hemin and mesoporous carbon hybrid electrocatalyst for the oxygen reduction reaction (ORR) is developed by using hemin as the Fe–N-containing precursor to control the chemistry of the metal and the chemical composition of the carbon surface. As a first step, Hemin is used as the Fe–N-containing precursor to prepare the Fe–N-doped mesoporous carbon (H-MC) via a nano-casting process by using sucrose as a carbon source and mesoporous silica as a hard template. Hemin is then used as the Fe–N₄-containing precursor to prepare H-MC supported hybrid catalyst. The Fe-doped and N-doped mesoporous carbons are also prepared and the catalytic properties of the prepared catalysts for ORR in alkaline media are investigated. The results show that as compared with the much more expensive Pt/C catalyst, the hybrid catalyst obtained in this work exhibits not only a higher onset potential, but also a higher current density.     

Uncertainty quantification of CO2 emission reduction for maritime shipping

The International Maritime Organization (IMO) has recently proposed several operational and technical measures to improve shipping efficiency and reduce the greenhouse gases (GHG) emissions. The abatement potentials estimated for these measures have been further used by many organizations to project future GHG emission reductions and plot Marginal Abatement Cost Curves (MACC). However, the abatement potentials estimated for many of these measures can be highly uncertain as many of these measures are new, with limited sea trial information. Furthermore, the abatements obtained are highly dependent on ocean conditions, trading routes and sailing patterns. When the estimated abatement potentials are used for projections, these ‘input’ uncertainties are often not clearly displayed or accounted for, which can lead to overly optimistic or pessimistic outlooks. In this paper, we propose a methodology to systematically quantify and account for these input uncertainties on the overall abatement potential forecasts. We further propose improvements to MACCs to better reflect the uncertainties in marginal abatement costs and total emissions. This approach provides a fuller and more accurate picture of abatement forecasts and potential reductions achievable, and will be useful to policy makers and decision makers in the shipping industry to better assess the cost effective measures for CO₂ emission reduction.     

Photocatalytic reduction of CO2 using TiO2 powders in supercritical fluid CO2

The photocatalytic reduction of CO₂ was investigated using TiO₂ powders in supercritical fluid CO₂. These were irradiated in a stainless steel vessel at 9.0 MPa and 35°C. After reducing the CO₂ pressure to the ordinary state, pure water was added to the vessel while avoiding air contamination. No gaseous reduction products were observed. Formic acid was obtained only in aqueous solution. The optimal irradiation time for the production of formic acid was 5 h. Addition of acidic solutions rather than pure water was preferable for formic acid formation. Formic acid seems to be produced through the protonation of reaction intermediates on TiO₂ powders in solutions. The CO₂-reduction system described here may be of practical value for efficient CO₂-conversion and fixation, storage of solar energy, and production of raw materials for the photochemical industry.     

Oil pricing policies and macroeconomy for an oil-based economy

This paper analyses the oil pricing policies for an oil-based economy within a national planning framework. It contains a total asset maximization problem in the non-oil sector and a macroeconomic model. The main conclusion is that Hotelling's r-percent rule fails to apply for an oil-based nation if the minimum-import constraint becomes binding. Therefore, the difference between the marginal revenue growth rate and the yield on domestic investment turns down when the import constraint is binding and then it goes through several cycles before it turns up as the constraint is non-binding over the planning horizon.     

Molecular engineering control defects within carbon nitride for optimized co-catalyst Pt induced photocatalytic CO2 reduction and NO2 oxidation reaction

We confirmed a specific copolymerization (molecular doping) method for the covalent integration of 2,4-dihydroxyoxazole (DHO) monomer within the framework of carbon nitride (CN). The obtained composites xCN/DHO reveal a sophisticated dual-phase photocatalytic activity, which can effectively reduce and oxidize the CO₂ and NO₂ sources in an aqueous solution and simultaneously performed the oxidation of olefin (CC) in an organic state. This momentous dual state activity is concerned with the lipophilicity elevation from the convolution of oxazole (DHO) monomer within the shell of CN semiconductor. This modulation demonstrates the probability of hydrophobic olefin molecules, escorted in the bulk of CN and associated with the oxidation of hydroxyl radicals (1OH) caused by photogenerated electrons/holes. In this approach, the olefinic compound allusively consumes the photoinduced electrons/holes through elevated CN/DHO, thus stimulating the entire photocatalytic route. Recent research provides a novel strategy for the production of solar fuels upon organic synthesis via the oxidizing capacity of photoinduced holes within free semiconductors of amphiphilic metals. Likewise, the results of the NO₂ photocatalytic reaction demonstrated that molecular doping drastically reduces the oxidative capacity and improves its reducing propensity. More importantly, the CO₂ reduction process supervenes into an extreme aggregation of methane (CH₄) as well as carbon monoxide (CO) in the presence of co-catalyst Pt respectively. The photocatalytic results demonstrate that the copolymerized CN provide the greatest reduction/oxidation potential, which is due to its chemical oxidation phase that causes superior fluctuations in whole performance under solar irradiation.     

High efficiency photocatalytic CO2 reduction realized by Ca2+ and HDMP group Co-modified graphitic carbon nitride

The development of highly efficient and visible-light responsive carbon nitride (CN) photocatalysts is desirable to address energy shortages and environmental pollution challenges. Herein, we synthesized novel 2-hydroxy-4,6-dimethylpyrimidine (HDMP) group and Ca²⁺ co-modified carbon nitride (CN) photocatalyst (CN-CAA) using a facile in situ copolymerization procedure employing urea and calcium acetylacetonate (CAA) as precursors. The HDMP group and Ca²⁺ co-modification contributed to increased electron density and modulated electronic structure, resulting in extended visible light harvesting and accelerated separation and migration of photoinduced charge carriers. Benefiting from the enhanced visible light utilization and improved photoexcited carriers separation and transportation, the CN-CAA exhibited significantly elevated visible-light-driven photocatalytic activity for CO₂ reduction. This work provided a new insight into the photocatalytic performance promotion of CN through molecular engineering and metal ions incorporation co-modification.     

Photo-induced CO2 reduction by hydrogen for selective CO evolution in a dynamic monolith photoreactor loaded with Ag-modified TiO2 nanocatalyst

Ag-promoted TiO₂ nanoparticles immobilized over the cordierite monolithic support for dynamic and selective photo-reduction of CO₂ to CO by the use of hydrogen has been investigated. Ag-loaded TiO₂ NPs synthesized by a facile sol–gel method were coated over the monolith channels by dip-coating method. The samples were characterized by XRD, Raman, FTIR, SEM, TEM, XPS, N₂ adsorption–desorption, UV–Vis and PL spectroscopy. The photo-activity test of Ag-modified TiO₂ NPs was conducted for dynamic photocatalytic CO₂ reduction with H₂ as a reductant via a reverse water gas shift (RWGS) reaction in a cell type and monolith photo-reactors. Using 5 wt. % Ag/TO₂ NPs, CO₂ was energetically converted to CO with a yield rate 1335 μmole g-catal.^?1 h^?1, a 111 fold-higher than the amount of CO produced over the pure TiO₂ catalyst. More importantly, photo-activity of Ag/TiO₂ catalyst for CO evolution can be improved by 209 fold using monolith photo-reactor than the cell type reactor under the same operating conditions. This enactment was evidently due to the efficient light harvesting with larger illuminated surface area inside monolith micro-channels and efficient charges separation in the presence of Ag-metal. The reusability of Ag/TiO₂ NPs loaded over the monolithic support showed favorable recycling capability than the catalyst dispersed in a cell reactor. A possible reaction mechanism for this observation has been discussed in detail.     

Nitrogen-doped carbon nanotubes with high activity for oxygen reduction in alkaline media

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a floating catalyst chemical vapour deposition method. The multiwalled NCNT contains 8.4 at% nitrogen and has a dimension of 100 nm in the diameter and 10-20 nm in the wall thickness. The catalytic activity and durability of the NCNTs towards oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in KOH solution. In addition, the effects of KOH concentration on several ORR performance indicators of the NCNT catalyst, such as the number of electrons transferred, the diffusion-limiting current density, the onset and half-wave potentials, were also examined in electrolytes of various KOH concentrations, ranging from 0.1 to 12 M. Experimental results show that NCNTs exhibited comparable activity for ORR in alkaline electrolyte as compared with commercially available Pt/C catalyst, and much higher activity than commercial Ag/C catalysts. In addition, the NCNTs showed good stability from the potential cycling test, and the concentration of KOH had significant impact on the ORR performance indicators of the NCNT catalysts.     

Effect of nickel on combustion synthesized copper/fumed-SiO2 catalyst for selective reduction of CO2 to CO

In this study, we explore the effect of nickel incorporation in Cu/fumed-SiO₂ catalyst for CO₂ reduction reaction. Two catalysts, Cu and CuNi supported on fumed silica were synthesized using a novel surface restricted combustion synthesis technique, where the combustion reaction takes place on the surface of the inert fumed-SiO₂ support. An active solution consisting of a known amount of metal nitrate precursors and urea (fuel) was impregnated on fumed silica. The catalyst loading was limited to 1 wt% to ensure localized combustions on the surface of fumed-SiO₂ by restricting the combustion energy density. The synthesized catalysts were tested for CO₂ hydrogenation reaction using a tubular packed bed reactor between temperature 50°C and 650°C, where Cu/SiO₂ showed high CO₂ conversion to carbon monoxide, and the addition of Ni further improved the catalytic performance and showed some tendency for methane formation along with CO. Moreover, both the catalysts were highly stable under the reaction conditions and did not show any sign of deactivation for ~42 hours time on stream (TOS). The catalysts were characterized using X-ray diffractometer (XRD), scanning electron microscope/energy dispersive X-ray spectrometer (SEM/EDX), transmission electron microscope (TEM), and the Brunauer-Emmet-Teller (BET) surface area measurement technique to understand their structural properties and to assess the effect of CO₂ conversion reaction. In situ DRIFTS was also used to investigate the reaction pathway followed on the surface of the catalysts.     

Optimal policies for investment and depletion in an oil-rich industrialized economy

There seems to be a tendency to determine the rate of oil extraction independently of the decisions to invest the proceeds of the resource. This paper sets out a general framework whereby the two policy variables can be analysed jointly. The methodology proposed is one of optimal control theory combined with a long-run macroeconomic model. The model presented here is structured with special reference to the UK economy but it can be applied, with the necessary modifications to any industrialized economy, with flexible exchange rate.     

LDHs-based bifunctional electrocatalyst for effective tunable syngas generation via CO2 reduction

Electrocatalytic reduction of CO₂ into syngas (CO and H₂) has been recognized to be a promising approach to achieve carbon neutrality. However, producing syngas with tunable H₂/CO ratios in a wide range is still challenging. Herein, nitrogen doped graphene aerogel (GA) supported both single-atomic Ni and Ni nanoparticles (NPs) with a surface atomic ratio of 1.11 were constructed by using layered double hydroxide (LDHs) and g-C₃N₄ as Ni and N precursors, respectively. H₂ and CO are the only products of CO₂ electroreduction and the ratio of H₂/CO can be tuned from 0.4 to 2.5 by changing applied potentials. In addition, the catalyst exhibits a large CO Faradaic efficiency (74%) and good long-term stability (12 h) at a relatively small potential (?0.67 V vs. RHE). This study will shed a new light on the construction of bifunctional catalysts for efficient tunable syngas generation via electroreduction of CO₂.     

Inter-factor/inter-fuel substitution,carbon intensity,and energy-related CO2 reduction: Empirical evidence from China

Carbon dioxide (CO₂) reduction, which is the central issue in addressing global warming, depends on the extent that clean energy can substitute for CO₂ emitting coal and non-energy factors can substitute for energy factor. The purposes of this paper are to empirically investigate inter-factor/inter-fuel substitution in China and to evaluate the determinants of China's energy-related carbon intensity as well as mitigation effects of carbon tax. Considering China's rapid increase in energy consumption and the slow adjustment in substitution, the two-stage estimation method and the dynamic error correction mechanism are employed in this study. The empirical results suggest substitutability among different types of energy sources as well as substitutability among energy, labor, and capital. The magnitude of cross-price elasticities indicates that the substitutions are inelastic, which limits the scope of the Chinese government to implement substitution strategy aiming at energy conservation and environmental management. China's carbon intensity declined during 1985–2012, most of which can be attributed to labor substitution and energy price increase. However, carbon-intensive technology being embodied in China's capital investment (energy consuming equipment) has contributed to the increase in carbon intensity. A carbon tax of RMB 50/tonne could reduce 332.9 million tonnes CO₂ emissions on the basis of 2012. In addition, if ignoring the feedback between inter-factor/inter-fuel substitutions, CO₂ mitigation potential would be underestimated.     

Single transition metal atom catalysts on Ti2CN2 for efficient CO2 reduction reaction

Electrochemical CO₂ reduction reaction (CO₂RR) is an efficient way in the utilization of CO₂. In this work, single transition-metal (TM) atom (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) anchored on two-dimensional (2D) Ti₂CN₂ are designed for CO₂RR using density-functional-theory (DFT) calculation. We show that Ti₂CN₂ serves as an excellent substrate to support single atom catalysts (SACs), compared to Ti₂CO₂ and Ti₂CF₂. We find that the Sc, Ti and V supported on Ti₂CN₂ show high catalytic activities to produce CO with a low overpotential of 0.37, 0.27, and 0.23 eV, respectively. Differently, the Mn and Fe on Ti₂CN₂ are catalytically active for the production of HCOOH with a low overpotential of 0.32 and 0.43 eV, respectively. We further show that the negatively charged TM-Ti₂CN₂ can capture and activate CO₂ more effectively, and the catalytic activity and selectivity can be significantly tuned by injecting extra electrons.