Water Gas Shift Activity Research Articles

Unravelling the active sites and structure-activity relationship on Cu–ZnO–Al2O3 based catalysts for water-gas shift reaction

Herein, we investigated the main active sites and structure-sensitivity of the water-gas shift (WGS) reaction over ternary Cu–ZnO–Al2O3 (CZA) catalysts. CZA catalysts with various Cu contents were synthesized by the homogeneous one-step coprecipitation method. The Cu content mainly affected the number of active Cu sites and was closely related to the WGS activity. Turnover frequency (TOF) values were independent of Cu dispersion, indicating that the CZA catalyst is structure-insensitive in WGS. The ratio of surface Cu+ species also strongly influenced the activity of the CZA catalyst. TOF based on the total active Cu species showed a constant value, but the CO conversion was linearly increased with the number of surface Cu+ species.

Enhanced water-gas shift reaction performance of MOF-derived Cu/CeO2 catalysts for hydrogen purification

The water-gas shift (WGS) reaction has received renewed interest because it is one of the key reactions for producing hydrogen and renewable energy in contemporary technologies like fuel cells and bio-refineries. Catalysts play an important role in WGS reaction for achieving high CO conversion and hydrogen generation activity. Thus, the performance and stability of catalysts are vital for the WGS reaction. In the present work, the CuCe metal-organic framework (MOF) is used as a template to derive the nanostructured Cu/CeO2 catalyst. The influence of CuCe-MOF templated approach on the WGS activity of Cu/CeO2 has been established. Different Cu doping levels had a significant impact on WGS activity. Amongst, the Ce0.8Cu0.2O2 (Cu2Ce) catalyst had a highest CO conversion (96%). The long-term stability tests further prove that the Cu2Ce catalyst had maintained high CO conversion over 100 h reaction time. XRD and TEM results suggest that different loadings of Cu content have a distinct impact on the dispersion of Cu and the catalytic properties. N2O chemisorption results suggest that 20 wt.% of Cu loading resulted in high Cu dispersion (52%) compared to other loadings. The H2-temperature programmed reduction (TPR) revealed that the superior catalytic activity of Cu2Ce catalyst could be attributed to the strong reducibility (i.e. lower redox temperature) derived from CuCe-MOF template. It further suggests well-dispersed copper oxide species at low Cu loadings and crystalline copper oxide species at high Cu loadings. This work emphasizes the significance of Cu/CeO2 catalysts with exceptional catalytic activity and stability for the WGS process with MOF-precursor.

A Study of Support Effects for the Water-Gas-Shift Reaction over Cu

The water–gas-shift (WGS) reaction was studied on a series of supported Cu catalysts in which the MgAl2O4 (MAO) support was modified by depositing ZnO, CeO2, Mn2O3 and CoO using Atomic Layer Deposition (ALD). Addition of Cu by one ALD cycle gave rise to catalysts with nominally 1-wt% Cu. A 1.1-wt% Cu/MAO catalyst prepared by ALD exhibited twice the dispersion but ten times the WGS activity of a 1-wt% Cu/MAO catalyst prepared by impregnation, implying that the reaction is structure sensitive. However, Cu catalysts prepared with the ZnO, CeO2, and Mn2O3 films showed negligible differences from that of the Cu/MAO catalyst, implying that these oxides did not promote the reaction. Cu catalysts prepared on the CoO film showed a slightly lower activity, possibly due to alloy formation. The implications of these results for the development of better WGS catalysts is discussed.

Role of interfacial oxygen vacancies in low-loaded Au-based catalysts for the low-temperature reverse water gas shift reaction

Gold-based catalysts have shown high catalytic activity for reverse water gas shift (RWGS) reactions at low temperatures. Despite extensive studies, the RWGS reaction on Au-based catalysts with very low Au content (< 0.1 wt%) has not yet been investigated. In this study, TiO2 and ZrO2 supported gold catalysts with such low gold loading have been synthesized and tested for RWGS. The catalysts were investigated by a series of in/ex-situ characterization techniques, including ICP-OES, XRD, BET, XPS, STEM, STEM-EELS, TAP, in-situ DRIFTS and in-situ EPR. At 250 oC, the Au/TiO2 catalyst showed almost 10 times higher activity than Au/ZrO2. In-situ DRIFTS results suggest that the formate mechanism is the predominant mechanism over Au/ZrO2, while over Au/TiO2 the reaction proceeds via the formation of hydroxycarbonyl intermediates. A combined study including STEM, STEM-EELS, XPS, and in-situ EPR suggests that the interfacial Au–Ov–Ti3+ sites are responsible for the superior activity of Au/TiO2.

Ptn–Ov synergistic sites on MoOx/γ-Mo2N heterostructure for low-temperature reverse water–gas shift reaction

In heterogeneous catalysis, the interface between active metal and support plays a key role in catalyzing various reactions. Specially, the synergistic effect between active metals and oxygen vacancies on support can greatly promote catalytic efficiency. However, the construction of high-density metal-vacancy synergistic sites on catalyst surface is very challenging. In this work, isolated Pt atoms are first deposited onto a very thin-layer of MoO3 surface stabilized on γ-Mo2N. Subsequently, the Pt–MoOx/γ-Mo2N catalyst, containing abundant Pt cluster-oxygen vacancy (Ptn–Ov) sites, is in situ constructed. This catalyst exhibits an unmatched activity and excellent stability in the reverse water-gas shift (RWGS) reaction at low temperature (300 °C). Systematic in situ characterizations illustrate that the MoO3 structure on the γ-Mo2N surface can be easily reduced into MoOx (2 < x < 3), followed by the creation of sufficient oxygen vacancies. The Pt atoms are bonded with oxygen atoms of MoOx, and stable Pt clusters are formed. These high-density Ptn–Ov active sites greatly promote the catalytic activity. This strategy of constructing metal-vacancy synergistic sites provides valuable insights for developing efficient supported catalysts.

Inhibition of water-gas shift reaction activity of oxide-supported Pt catalyst by H2 and CO2

A catalyst composed of platinum-group metals supported on an oxide exhibits high activity in a low-temperature water-gas shift (LT-WGS) reaction; however, the reaction rate is greatly reduced when H2 or CO2, the product gases of the WGS reaction, are included in the reactant stream. In this study, we attempted to understand the origin of this activity inhibition by analyzing the kinetic data with in-situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The WGS reaction rate decreases more severely by H2 than CO2. The CO-DRIFTS spectra indicate that this can be explained by H2 preoccupying the active sites for the WGS reaction. In addition, by comparing the kinetic data with the literature, it could be inferred that a similar inhibition mechanism is operating in other oxide-supported Pt catalysts. Considering this inhibition mechanism will be important for the development of catalysts with high WGS activity in reformate gas.

Theoretical and experimental insights into CO2 formation on Co2C catalysts in syngas conversion to Value-Added chemicals

Cobalt carbide (Co2C) has been discovered as the promising active phase for Fischer–Tropsch to olefins (FTO) process and higher alcohols synthesis (HAS) from syngas, in the form of nanoprisms and nanospheres, respectively. However, CO2 formation is inevitable on Co2C catalysts, especially in FTO process. So far, the mechanism of CO2 formation on Co2C surfaces is less understood. This work provides fundamental insights into CO2 formation on Co2C nanospheres and nanoprisms through computational and experimental study. DFT calculations demonstrate that: Co2C (101) and (020) surfaces exposed on Co2C nanoprisms are basically not active for water gas shift (WGS) reactions but the introduction of Na greatly promotes CO2 formation. CO2 is less favored on Co2C(111) surface which is dominant on Co2C nanospheres, however, the reverse WGS activities can be promoted with Na addition. The experimental results confirmed removing Na from Co2C can efficiently suppress WGS activity, thus reducing CO2 selectivity while the selectivity of light olefins retained. Though previous studies focused on Na addition to promote the yield of light olefins, our work indicates that Na also promotes undesired CO2 formation. Our results suggest that Na is crucial for active phase formation but not necessarily beneficial during the CO hydrogenation reactions.

Structure-Activity Relationship of Ceria Based Catalyst for Hydrogen Production

T he role of Sm addition on water gas shift performance of Re/ceria was studied. A redox cycle between Ce4+ and Ce3+ of ceria support by oxygen vacancies generation is one of the elementary step in water gas shift mechanism. In this work, we have attempted to enrich the Ce3+ content at the ceria surface of Re/doped ceria to enhance the water gas shift performance. The water gas shift reaction was carried out over Re/Sm-doped ceria catalysts with different contents of Sm (0, 5, 10, 15 wt%). The H2-TPR explained the activity enhancement of these catalysts due to Sm addition which have lowered the reduction temperature of rhenium oxide species and promoted the surface of ceria. The results of water gas shift activity investigation presented that the activity of 1%Re/Ce10%SmO was higher than that of other catalysts. The influence of Sm on increasing the catalytic activity of Re catalysts is concluded to be from enhancing the Ce3+ content which then facilitate the redox process at the surface.

Role of percentage of {0 0 1} crystal facets in TiO2 supports toward the water–gas shift reaction over Au-TiO2 catalysts

Support effects always attract extensive interesting in heterogenous catalysis. However, the same supports might not show same effects on different catalytic reactions, even the opposite. Here, we quantitatively analyzed the role of the percentage of {001} facets toward the water–gas shift (WGS) catalytic performances over Au-TiO2 catalysts. With increasing HF, the percentage of {001} gradually increase, while their catalytic activities gradually decrease following the sequence: Au-TiO2-HF0 > Au-TiO2-HF3 > Au-TiO2-HF9. For cyclic stability, Au-TiO2-HF0 showing somewhat low stability is due to increase in percentage of {001}, while Au-TiO2-HF3 and Au-TiO2-HF9 having high stability is because of decrease in the percentage of {001} albeit Au particle sintering. Accordingly, WGS activities of both fresh and used catalysts have good linear correlation with the percentage of {001} (negative correlation), the percentage of oxidized gold species (positive correlation) and the hydrogen consumption (positive correlation).

Exploring the role of promoters (Au, Cu and Re) in the performance of Ni–Al layered double hydroxides for water-gas shift reaction

Water-gas shift (WGS) reaction is well-known industrial process targeting hydrogen production. Designing well-performing and economically profitable WGS catalysts is the key toward production of pure hydrogen for application in fuel cell processing systems. Promotional role of Au, Cu, or Re in the WGS performance of Ni–Al formulations derived from hydrotalcite precursor was analysed on the basis of deep characterization by BET, XRD, UV–Vis, XPS, and TPR measurements of as-prepared and WGS-tested samples. Additionally, modification by ceria was examined. WGS results revealed that catalyst behaviour was strongly dependent on promoter type. The best performance exhibited gold-promoted Ni–Al layer double hydroxide modified with ceria. This system showed a superior catalytic activity as 99.7% CO conversion at 220 °C that correlated well with significantly enhanced reducibility of support. Although Au-containing CeO2-modified Ni–Al catalyst outperformed WGS activity of Cu- and Re-promoted analogues, stability of Re-containing sample and enhanced activity of Cu-based sample after tests at different reaction conditions manifested promising results. They leave open space for future investigations addressing improved catalyst performance by tuning Re4+/Re7+ redox structures or optimizing catalyst composition.

Cu-Y2O3 Catalyst Derived from Cu2Y2O5 Perovskite for Water Gas Shift Reaction: The Effect of Reduction Temperature

Cu2Y2O5 perovskite was reduced at different temperatures under H2 atmosphere to prepare two Cu-Y2O3 catalysts. The results of the activity test indicated that the Cu-Y2O3 catalyst after H2-reduction at 500 °C (RCYO-500) exhibited the best performance in the temperature range from 100 to 180 °C for water gas shift (WGS) reaction, with a CO conversion of 57.30% and H2 production of 30.67 μmol·gcat−1·min−1 at 160 °C and a gas hourly space velocity (GHSV) of 6000 mL·gcat−1·h−1. The catalyst reduced at 320 °C (RCYO-320) performed best at the temperature range from 180 to 250 °C, which achieved 86.44% CO conversion and 54.73 μmol·gcat−1·min−1 H2 production at 250 °C. Both of the Cu-Y2O3 catalysts had similar structures including Cu°, Cu+, oxygen vacancies (Vo) on the Cu°-Cu+ interface and Y2O3 support. RCYO-500, with a mainly exposed Cu° (100) facet, was active in the low-temperature WGS reaction, while the WGS activity of RCYO-320, which mainly exposed the Cu° (111) facet, was greatly enhanced above 180 °C. Different Cu° facets have different abilities to absorb H2O and then dissociate it to form hydroxyl groups, which is the main step affecting the catalytic rate of the WGS reaction.

Structure–performance correlations in the hybrid oxide-supported copper–zinc SAPO-34 catalysts for direct synthesis of dimethyl ether from CO2

Growing CO2 emissions lead to global warming, which is currently one of the most challenging environmental phenomena. Direct catalytic hydrogenation to dimethyl ether over hybrid catalysts enables CO2 utilization, hydrogen and energy storage and produces sustainable fuels and an important platform molecule. In this paper, we evaluated structure–performance correlations in the bifunctional hybrid copper–zinc SAPO-34 catalysts for direct synthesis of dimethyl ether via CO2 prepared using zirconia, alumina and ceria used as oxide carriers. Higher copper dispersion and higher CO2 conversion rate were uncovered over the alumina and zirconia supported catalysts followed by ceria supported counterpart. The CO2 hydrogenation seems to be principally favoured by higher copper dispersion and to a lesser extent depends on the concentration of Bronsted acid sites in the studied catalysts. Because of lower reverse water gas-shift activity, the alumina supported catalyst exhibited a higher dimethyl ether yield compared to the zirconia and ceria supported counterparts.

Effect of support preparation method on water-gas shift activity of copper-based catalysts

Reducing the effect of global warming and increasing the needs for fuel sources appoint hydrogen utilization in fuel cell technology a very promising demand. A step for required pure hydrogen production for this purpose is the water-gas shift (WGS) reaction and the design of well performing but cost effective WGS catalysts, the latter being of growing research interest. In the present study catalysts containing copper (3 wt%) supported on ceria/alumina (30 wt% ceria) and Y-doped ceria/alumina (1 wt% Y2O3 regarding ceria content) were prepared by impregnation (IM) and by mechanochemical mixing (MM). The effect of support synthesis methods on the performance in the WGS reaction was discussed based on catalyst characterization by means of XRD, HRTEM, XPS, and H2-TPR methods. It was established that the effect of Y-doping was strongly dependent on the method of support preparation being positive for MM and unfavourable in the case of impregnation. The IM method caused the formation of a superficial phase with CuO, Y-dopant, and ceria in close location. Additionally, a higher amount of oxygen vacancies was related to non-reducible Y3+ ions that interrupted Cu–oxygen vacancy–Ce interaction thus leading to both lower reducibility and WGS activity. The presence of yttria phase located on ceria-free alumina in the case of MM support decreased the negative influence of Ce3+ replacement by Y3+ ions. A positive effect of separate Y2O3 could explain the best WGS performance observed. Long-term WGS tests showed good stability thus making this catalyst promising composed mainly of alumina and low amount of active phases. The study contributes to the development of an advantageous formulation of well-performing and economically profitable WGS catalysts for efficient improving of hydrogen purity for small-scale applications.

Au and Pt Remain Unoxidized on a CeO2-Based Catalyst during the Water-Gas Shift Reaction.

The active forms of Au and Pt in CeO2-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO2 oxygen vacancies at the metal-CeO2 interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt0, Au0 nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process.

Autothermal Reforming of Acetic Acid to Hydrogen and Syngas on Ni and Rh Catalysts

The autothermal reforming (ATR) of acetic acid (HAc) as a model bio-oil compound is examined via bench scale experiments and equilibrium modelling to produce hydrogen and syngas. This study compares the performance of nickel (Ni-Al, Ni-CaAl) vs. rhodium (Rh-Al) for particulate packed bed (PPB), and of Rh-Al in PPB vs. Rh with and without Ceria for honeycomb monolith (‘M’) catalysts (R-M and RC-M). All PPB and M catalysts used Al2O3 as main support or washcoat, and when not pre-reduced, exhibited good performance with more than 90% of the HAc converted to C1-gases. The maximum H2 yield (6.5 wt.% of feed HAc) was obtained with both the Rh-Al and Ni-CaAl catalysts used in PPB, compared to the equilibrium limit of 7.2 wt.%, although carbon deposition from Ni-CaAl at 13.9 mg gcat−1 h−1 was significantly larger than Rh-Al’s (5.5 mg gcat−1 h−1); close to maximum H2 yields of 6.2 and 6.3 wt.% were obtained for R-M and RC-M respectively. The overall better performance of the Ni-CaAl catalyst over that of the Ni-Al was attributed to the added CaO reducing the acidity of the Al2O3 support, which provided a superior resistance to persistent coke formation. Unlike Rh-Al, the R-M and RC-M exhibited low steam conversions to H2 and CH4, evidencing little activity in water gas shift and methanation. However, the monolith catalysts showed no significant loss of activity, unlike Ni-Al. Both catalytic PPB (small reactor volumes) and monolith structures (ease of flow, strength, and stability) offer different advantages, thus Rh and Ni catalysts with new supports and structures combining these advantages for their suitability to the scale of local biomass resources could help the future sustainable use of biomasses and their bio-oils as storage friendly and energy dense sources of green hydrogen.

CeO2‐TiO2 Hybid‐Nanotubes with Tunable Oxygen Vacancies as the Support to Confine Pt Nanoparticles for the Low‐Temperature Water‐Gas Shift Reaction

AbstractReducible oxides as supports have been demonstrated to improve the activity of Pt catalysts towards water‐gas shift (WGS) reaction. The Pt species anchored by the oxygen vacancies derived from these supports play as catalytic sites during low‐temperature WGS reaction. Herein, we introduced CeO2 to modify TiO2 nanotubes (TiO2NT) and prepared CeO2‐TiO2 hybid‐nanotubes ((CeO2)x(TiO2)1‐xNT, x=0.2, 0.4, 0.6) to confine Pt nanoparticles (NPs) as the efficient catalysts for the low‐temperature WGS reaction. Pt NPs confined in (CeO2)x(TiO2)1‐xNT catalysts exhibit higher WGS activity than that of the Pt NPs entrapped in pure TiO2NT (Pt‐in‐TiO2NT) and Pt/CeO2 catalysts throughout the entire reaction temperature range. Activity measurements coupled with the physicochemical characterization of catalysts suggest that the redox ability of PtOx species is positive correlated with WGS activity and oxygen vacancy adjacent to Pt (Pt‐Ov) serves as the active site for H2O dissociation and CO oxidation in WGS reaction.

A new application of the commercial high temperature water gas shift catalyst for reduction of CO2 emissions in the iron and steel industry: Lab-scale catalyst evaluation

In this study, we present a detailed investigation of a commercial iron-based high temperature water gas shift (HTWGS) catalyst (Johnson Matthey KATALCOTM 71-6) in a new application: the production of hydrogen from blast furnace gas (BFG), which originates from iron and steel manufacturing. During the lab-scale catalytic testing under BFG conditions the catalyst demonstrated: 1) high water gas shift activity and stability; 2) minimal methanation at reduced steam to CO ratios; 3) high resistance towards H2S impurities present in the feed. The results of post-characterization of the discharged samples confirm the robustness of KATALCO 71-6 towards BFG process conditions: no over-reduction of the catalytically active Fe3O4 phase and no formation of a less active FeS phase. An in situ X-ray absorption spectroscopy study revealed no over-reduction of the iron phase under BFG conditions and the stabilization of the iron phase by diffusion of chromium into the iron oxide matrix. The findings of this study demonstrate the suitability of the iron-based HTWGS catalyst KATALCO 71-6 for the production of hydrogen from BFG streams. Knowledge gained in this study is an essential step in the development and scale up of carbon capture and storage as well as carbon capture and utilization technologies, such as the sorption enhanced water gas shift (SEWGS) technology, aimed at reducing the CO2 footprint during steel manufacturing.

Enhancement of hydrogen production using Ni catalysts supported by Gd-doped ceria

A redox cycle between Ce4+ and Ce3+ is an elementary step in water gas shift (WGS) mechanism. By facilitating the redox cycle between +4 and +3 of cerium, a formation of oxygen vacancy can be enhanced. It is considered to be a dominating factor in developing the WGS performance and the stability of ceria in this work. We have facilitated the redox cycle in CeO2 to enrich the WGS activity. The WGS reaction was carried out on Ni catalyst supported by Gd-doped ceria (GDC) from Daiichi. Ni and Re were added onto GDC by impregnation method to examine the role of Re addition on surface, structural and reducibility, which affected upon their catalytic activities. Rhenium has an influence on increasing the water gas shift performance of Ni/GDC catalysts because it facilitates the redox process at the surface of ceria, disperses Ni particles and enhances oxygen vacancy formation. The results indicate that the water gas shift activity of 1%Re4%Ni/GDC is higher than that of 5%Ni/GDC. The dispersion of active site on the surface of catalyst results in an increase of CO molecule adsorption and acceleration of the redox cycle between Ce4+ and Ce3+ of ceria support via oxygen vacancy generation. Therefore, using a combination of these two effects can enhance the WGS performance.

Mechanism insight into MnO for CO activation and O removal processes on Co(0001) surface: A DFT and kMC study

Direct production of olefins from syngas is of great energy and economic significance. Recently, many researches have reported that Mn modified Co based catalysts are of great application prospect. However, the effect mechanism of Mn is still not clear. This work illustrates how the addition of Mn promotes the CO dissociation and O removal processes by comparing Co(0001) surfaces with MnO/Co(0001) surfaces through density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. Specifically, CO tends to dissociate through the H-assisted path via CHO intermediate on both surfaces while direct dissociation may also occur on MnO/Co(0001). The addition of MnO can stabilize the transition states and reduce the reaction barrier by its bonding with the transition states in the direct dissociation path and CHO intermediate path, thus improving the dissociation efficiency significantly. Besides, instead of promoting the CO dissociation on Co(0001), the dissociation path via COH intermediate consumes the already dissociated C by its inverse reactions. On the contrary, MnO/Co(0001) can inhibit the reverse reactions of the COH intermediate pathway. The absorbed O tends to be removed as H2O through OH disproportionation path on both surfaces. The effect of temperature on the path of water generation is negligible. The low CO2 selectivity advantage of MnO/Co(0001) over Co(0001) becomes more and more apparent with the raise of temperature. The addition of Mn doesn’t change the benefit of low water gas shift activity on Co based catalysts.

Enhancement of Hydrogen Production Using Ni Catalysts Supported by Gd-Doped Ceria

A redox cycle between Ce4+ and Ce3+ is the elementary step in water gas shift (WGS) mechanism. Facilitating a redox cycle between +4 and +3 of cerium enhanced the formation of oxygen vacancy which is considered as a dominate factor for developing the WGS performance and stability of ceria material. Therefore, in this work, we have tried to facilitate the redox cycle in CeO 2 to enrich the WGS activity. The WGS reaction was carried out on Ni catalyst supported by Gd-doped ceria (GDC). Gd-doped ceria material from Daiichi was employed as support for water gas shift reaction. Ni and Re were added onto GDC by impregnation method to examine the role of Re addition on surface, structural and reducibility which was altered to their catalytic activities. An influence of rhenium on increasing the water gas shift performance of Ni/GDC catalysts since Re facilitating the redox process at the ceria surface, dispersing Ni particles and oxygen vacancy formation. The results of water gas shift activity tests presented that the activity of 1%Re4%Ni/GDC was higher than that of 5%Ni/GDC. The role of Re on improving the WGS activity was promoting the dispersion of active metal site on catalyst surface which result in increases CO molecules adsorption and accelerating a redox cycle between Ce4+ and Ce3+ of ceria support by oxygen vacancies generation. Therefore, the WGS performance can be enhanced by the combination of these two effects.