Small Ni Particles Research Articles

Effect of Ga-Promoted on Ni/Zr + Al2O3 Catalysts for Enhanced CO2 Reforming and Process Optimization

AbstractIn this study, zirconia-modified alumina support (S) was used to investigate Ga-promoted Ni catalysts for dry reforming of methane (DRM). The catalysts (Ni + (0–3) wt% Ga/S) were prepared using the wet impregnation method and calcined at 700 °C for 3 h. The inclusion of Ga enhanced the surface area, basicity, and metal-support interaction of the Ni-Ga/S catalysts. Smaller Ni particles containing Ga were seen in the TEM. The most active and stable catalyst was Ni + 2.0 Ga/S, having a conversion of 35% CO2 and 28% CH4 at 600 °C and displaying less (17%) carbon deposition. Furthermore, the DRM process was optimized by a mathematical model. The model determined the optimal conditions as follows: temperature (800 °C), gas flow rate (GHSV—30,000 ml h−1gcat−1), and methane to carbon dioxide ratio (1:1). The model predicts CH4 and CO2 conversions of 76.76% and 82.0%, respectively, and an H2/CO ratio of 1.02, compared to experimental results showing CH4 conversion at 74.56%, CO2 conversion at 83.25%, and an H2/CO ratio of 1.01. The model demonstrates excellent agreement with the experimental observations, exhibiting less than 3% error. Graphical Abstract

Facile synthesis of Ni-phyllosilicate assisted by polyacrylamide at room temperature for CO2 hydrogenation to methane

To elucidate the effect of solution viscosity on the synthesis of Ni-phyllosilicate, polyacrylamide was incorporated to create a viscous aqueous medium containing of sodium metasilicate, nickel nitrate and NH4F. The enhanced viscosity promotes the dispersion of the initial formed crystal seeds and the growth of Ni-phyllosilicate, culminating in a Ni-rich NiPs-RT-6 of a high Ni content of up to 55.2 wt%. Residual polyacrylamide elimination was accomplished via calcination, concurrently enhancing metal-support interaction. The as-synthesized samples display a nanoflower morphology with nanospheres overlaid with numerous thin nanosheets. The relatively small Ni particles around 5.7 nm were obtained after reduction even at a very high Ni loading, owing to its strong metal-support interaction. NiPs-RT-6 achieves a CO2 conversion of 75.9% at 450 °C, 0.1 MPa, 60 L g−1·h−1, which closely approximates thermodynamic equilibrium. The turn over frequency for CO2 (TOFCO2) was substantial, calculated at 3.7 × 10−3 s−1, accompanied by activation energy (Ea) of 80.6 kJ·mol–1. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) further disclosed that m-HCOO– serves as a crucial intermediate following a formate reaction pathway. With its high Ni content, finely distributed Ni particles, and strong metal-support interaction, NiPs-RT-6 demonstrates promising catalytic activity in CO2 methanation.

MOFs-derived Ni@ZrO2 catalyst for dry reforming of methane: Tunable metal-support interaction

Metal-support interaction (MSI) plays an important role in heterogeneous catalysis, that could be well regulated by many strategies. Here, Ni@ZrO2 catalysts were controllably synthesized by sacrificial Zr-MOFs template strategy, and were applied to the dry reforming of methane (DRM). Amongst, the Ni/ZrO2-B catalyst shows the best performance toward CH4 and CO2 conversion, H2/CO ratio, and stability, following by Ni/ZrO2-A and Ni/ZrO2C catalysts. The difference in catalytic performance should be ascribed to different synthetic strategy, resulting in different properties of Ni species and ZrO2 matrix, and interface interaction. It revealed that small Ni particles were benefit for CH4 activation, and strong MSI boosted CO2 activation, that could remain the Ni dispersion and thermal stability. This study is beneficial to the catalyst design in DRM reaction.

Ni supported on desilicated HZSM-5 as catalyst for biogas reforming

In this study, Ni/HZSM-5 catalysts containing 3.0 and 5.0 wt% of Ni were used to produce hydrogen-rich streams through the dry reforming of methane, with biogas serving as the raw material. The effect of a desilication treatment on catalyst performance was evaluated. The removal of Si resulted in an increase in mesoporous volume. Moreover, in situ XANES and in situ XRD analyses revealed the formation of Ni2+ species with lower reducibility for desilicated samples. This was likely attributed to the presence of Ni2+ species confined within mesopores, promoting metal-support interaction, which leads to a higher metal dispersion, after reduction. The presence of small Ni particles resulted in a higher methane conversion and a low carbon formation during dry reforming of methane, regardless of nickel content.

Ni0+ particle size-dependent pyrolytic reforming of toluene over Ni/Al2O3 for the co-production of hydrogen and CNTs

Pyrolytic reforming of toluene over Ni-based catalysts loaded on nano-sized and micro-sized γ-Al2O3 is investigated in a fixed bed reactor under the temperature from 500 °C to 800 °C. The physicochemical properties of γ-Al2O3 and Ni/Al2O3 catalysts were characterized by HRTEM, XPS, XRD and H2-pulse chemisorption. The metal Ni loaded on micro-sized γ-Al2O3 gave the steady toluene conversion of more than 80% and graphite yield of 87.3% after 1 h of reforming reaction. The rapid decrease of H2 yield from 5.2 mmol/g-toluene to 0.4 mmol/g-toluene over Ni/nano-Al2O3 was obtained during the 1 h of reforming reaction at 500 °C. The particle size of metal Ni over nano-sized and micro-sized γ-Al2O3 were centered at 7.8 nm and 28.8 nm, respectively. The metastable NiCx crystallites were observed over the spent Ni/nano-Al2O3 catalyst, while only metal Ni were obtained over the spent Ni/micro-Al2O3 catalyst. Ni0+ particle size-dependent crystalline phase was evidenced by MD simulations, where incorporation of more carbon atoms was achieved on small Ni particles. The energy barrier for –CH2 dehydrogenation over Ni32C, Ni4C and Ni3C were estimated to be 90.2, 105.1 and 116.0 kJ/mol through the DFT simulation, respectively. It can be concluded that the crystalline Ni phase was maintained over Ni/micro-Al2O3 with large Ni particle size, prolonging the catalytic endurance and promoting the CNTs (Carbon Nanotubes) growth without the deposition of unexpected amorphous carbon.

CO2 methanation with high-loading mesoporous Ni/SiO2 catalysts: Toward high specific activity and new mechanistic insights

In the power-to-gas scenario, surplus renewable electricity is stored in the form of methane, by reacting green hydrogen with waste CO2 through the Sabatier reaction. Low-cost catalysts that feature a high activity at low temperature are needed. We disclose the sol–gel preparation of high-loading mesoporous Ni/SiO2 catalysts. (HR)-TEM, XRD, N2 physisorption, and H2 chemisorption show that small Ni particles (<5 nm) are obtained, even at loading up to 38 wt%. The best catalyst reached a specific activity of 10.2 µmolCH4.g−1.s−1 at 250 °C (TOF = 0.0155 s−1; almost 3 times higher than a reference catalyst prepared by impregnation). Being based on inert silica, these catalysts are ideal model materials to elucidate the reaction mechanism on nickel. Combining CO2-TPD, in-situ CO2-DRIFTS, and TPSR with DFT calculations, we show that CO2 methanation follows mostly the RWGS + CO-hydrogenation and the formate pathways, the former being dominant at low temperature.

Insight into the role of preparation method on the structure and size effect of Ni/MSS catalysts for dry reforming of methane

Dry reforming of methane (DRM) is considered a promising process to convert CH4 and CO2 into syngas for achieving carbon neutrality. However, sintering and carbon deposition of Ni pose significant challenges to the industrialization of DRM. The size of Ni particles significantly affects the generation of carbon deposits. In this study, a series of Ni/MSS catalysts were prepared using four different methods, including common impregnation, glycine-assisted impregnation, ethylene glycol-assisted impregnation and ammonia evaporation. The effects of preparation methods on the anti-sintering and anti-coking properties were explored through various characterization techniques. Results showed that glycine-assisted impregnation and ethylene glycol-assisted impregnation effectively improved the dispersion of Ni, resulting in small Ni particles while preserving the unique pore structure of MSS supports. Smaller Ni particles expose more active sites, which facilitate the resistance to carbon accumulation. These catalysts show the highest activity and excellent stability. The catalyst prepared by ammonia evaporation showed the best stability due to the synergistic effect of the strongest basicity and metal-support interaction. However, nickel phyllosilicate generation consumed a small amount of MSS, resulting in reduced specific surface area. Compared with the common impregnation method, the other three methods reduced the particle size of Ni and improved the interaction between support and metal, effectively enhancing the ability of the catalyst to resist coking and sintering. Kinetic studies also showed a significant decrease in the apparent activation energy of methane and carbon dioxide cracking due to the reduced particle size of Ni particles.

Anti-coking Ni encapsulated in SiO2 via one-pot reverse microemulsion method as a versatile catalyst for CO2 methane reforming

This paper reports the varying water-to-surfactant (ω) ratio in reverse microemulsion on the development of Ni encapsulation in bulk SiO2 catalyst for dry reforming of methane. From XRD and TEM analyses, the Ni particle size depends on the water-to-surfactant ratio. It found that an optimized ratio of ω improves the catalytic activity for the dry reforming of methane. The catalyst (Ni-SiO2-ω23) shows 70% CH4 conversion and 78% CO2 conversion at 700 °C and WHSV of 72000 mLgcat−1h−1 operating for 50 h with TOF of 12.6 s−1. It is highly anticipated that the increased fraction of 2:1 nickel phyllosilicate and small Ni particle size contributed to its improved catalytic activity corresponding to the ω ratio. Also, a higher ω value can resist carbon formation in the catalysts, characterized by XRD, TGA, Raman, XPS, and TEM. These results were encouraging that could be applied in similar high-temperature reactions.

Spillover Hydrogen on Electron-Rich Ni/m-TiO2 for Hydrogenation of Furfural to Tetrahydrofurfuryl Alcohol

Conversion of biomass-derived furfural (FFA) platform molecule to value-added tetrahydrofurfuryl alcohol (THFA) molecule is a sustainable route using an efficient non-noble metallic catalyst in water solvent. In this work, Ni in various loadings on mesoporous titanium dioxide (m-TiO2) was synthesized in one pot by Evaporation-Induced Self-Assembly (EISA). The synthesised catalysts were evaluated for the hydrogenation of furfural to tetrahydrofurfuryl alcohol. The catalysts were characterised using a combination of spectroscopic techniques such as XRD, H2-TPR, H2-TPD, XPS, SEM-EDX, TEM, and HR-TEM. The characterization results show that the Ni/m-TiO2 materials exhibit enhanced electron-rich active sites, facilitated hydrogen spillover, uniform dispersion of small Ni particles (~5 nm), and strong metal support interaction between Ni and TiO2. Among the various Ni dopings, 7.5 wt.% Ni/m-TiO2 catalyst exhibited the best performance and achieved 99.9% FFA conversion and 93.2% THFA selectivity in water solvent at 100 °C and under 2 MPa H2. Additionally, detailed kinetic studies, process parameters, the stability and reusability of the catalyst were also studied. The results demonstrated that the 7.5 wt.% Ni/m-TiO2 catalyst is highly active and stable.

Impact of preparation method on nickel speciation and methane dry reforming performance of Ni/SiO2 catalysts.

The methane dry reforming reaction can simultaneously convert two greenhouse gases (CH4 and CO2), which has significantly environmental and economic benefits. Nickel-based catalysts have been widely used in methane dry reforming in past decade due to their low cost and high activity. However, the sintering and coke deposition of catalysts severely limit their industrial applications. In this paper, three Ni/SiO2 catalysts prepared by different methods were systematically studied, and the samples obtained by the ammonia evaporation method exhibited excellent catalytic performance. The characterization results such as H2-TPR, XPS and TEM confirmed that the excellent performance was mainly attributed to the catalyst with smaller Ni particles, stronger metal-support interactions, and abundant Ni-O-Si units on the catalyst surface. The anti-sintering/-coking properties of the catalyst were significantly improved. However, the Ni/SiO2-IM catalyst prepared by impregnation method had uneven distribution of nickel species and large particles, and weak metal-support interactions, showing poor catalytic performance in methane dry reforming. Since the nickel species were encapsulated by the SiO4 tetrahedral network, the Ni/SiO2-SG catalyst prepared by sol-gel method could not expose more effective active sites even if the nickel species were uniformly dispersed, resulting in poor dry reforming performance. This study provides guidance for the preparation of novel anti-sintering/-coking nickel-based catalysts.

Size-Dependent Strong Metal–Support Interactions of Rutile TiO2-Supported Ni Catalysts for Hydrodeoxygenation of m-Cresol

A series of rutile TiO2-supported Ni catalysts with varying Ni sizes were prepared and reduced at 650 °C to explore the effect of Ni size on the strong metal–support interactions (SMSI) and its consequences on the hydrodeoxygenation (HDO) of m-cresol at 350 °C and atmospheric pressure. When the Ni size increases from 4 to 29.1 nm, the SMSI becomes stronger, e.g., the thickness of the TiOx overlayer and the coverage extent of TiOx on the Ni particle surface increase. Direct deoxygenation to toluene is the dominant pathway on Ni/TiO2 catalysts with varying Ni loadings, with almost no CH4 being formed. These results indicate that the TiOx overlayer significantly alters the property of Ni. That is, the C-C hydrogenolysis activity on bare Ni is completely inhibited due to SMSI, while the deoxygenation activity is improved at the Ni-TiOx interfacial perimeter sites. Meanwhile, the turnover frequency of HDO on small Ni particles of 4 nm is &gt; 2 times higher than that on large Ni particles of 29.1 nm, indicating that the small Ni particle with moderate SMSI appears to be optimal for the direct deoxygenation of m-cresol to toluene. The results suggest HDO activity may be enhanced by tuning the metal particle size and SMSI degree.

Constructing the highly efficient Ni/ZrO2/SiO2 catalyst by a combustion-impregnation method for low-temperature CO2 methanation

CO2 methanation is conducive to the storage of renewable electricity and the utilization of CO2. Exploiting highly efficient Ni-based catalysts with a simple method is of significance for this reaction. To achieve an excellent low-temperature activity, the attention is focused on the small Ni particles and ZrO2 promoter in this work, which can increase the amounts of H2 and CO2 active sites. Firstly, the simple combustion-impregnation method was employed, forming small Ni particles (about 6 nm). More metal-support interface and increased basicity could be generated in the meantime. Hence, the higher H2 dissociation and CO2 adsorption ability were attained. Secondly, ZrO2 serving as a promoter was beneficial to the formation of oxygen vacancies, which played an important role in CO2 activation and CH4 formation. These oxygen vacancies could weaken the CO bonds, improving the CO2 activation. In addition, they might serve as the H reservoir, increasing the H2 adsorption capacity. Because of the H spillover effect from Ni to ZrO2, the activated H atoms on Ni could react with activated CO2 to generate CH4. Therefore, with more active sites for H2 and CO2 activation, the Ni/ZrO2-COM catalyst exhibited the excellent catalytic performance at 300 °C. This work is of great significance in developing highly efficient Ni-based catalysts at low temperatures for CO2 methanation with a facile method.

Glycine-assisted preparation of highly dispersed Ni/SiO2 catalyst for low-temperature dry reforming of methane

Ni-based catalysts have been widely studied in reforming methane with carbon dioxide. However, Ni-based catalysts tends to form carbon deposition at low temperatures (≤600 °C), compared with high temperatures. In this paper, a series of Ni/SiO2-XG catalysts were prepared by the glycine-assisted incipient wetness impregnation method, in which X means the molar ratio of glycine to nitrate. XRD, H2-TPR, TEM and XPS results confirmed that the addition of glycine can increase Ni dispersion and enhance the metal-support interaction. When X ≥ 0.3, these catalysts have strong metal-support interaction and small Ni particle size. The Ni/SiO2-0.7G catalyst has the best catalytic performance in dry reforming of methane (DRM) test at 600 °C, and its CH4 conversion is 3.7 times that of Ni/SiO2-0G catalyst. After 20 h reaction under high GHSV (6 × 105 ml/gcat/h), the carbon deposition of Ni/SiO2-0.7G catalyst is obviously lower than that of Ni/SiO2-0G catalyst. Glycine-assisted impregnation method can enhance the metal-support interaction and decrease the metal particle size，which is a method to prepare highly dispersed and stable Ni-based catalyst.

Highly active Ni/CeO2/SiO2 catalyst for low-temperature CO2 methanation: Synergistic effect of small Ni particles and optimal amount of CeO2

CO2 methanation is of great significance to CO2 utilization. However, it is challenging to prepare Ni-based catalysts with superior low-temperature activity via a simple method. In this work, a highly active Ni/CeO2/SiO2 catalyst is developed by a combustion-impregnation method, and the synergistic effect of active sites for H2 and CO2 activation are studied. The research results show that highly dispersed Ni particles (6 nm) are obtained by this method with an instantaneous reaction. As a result of the increased number of Ni active sites, the catalyst exhibits improved catalytic activity. Moreover, addition of CeO2 promoter further improves the low-temperature activity. First, it enhances the catalyst reducibility, creating more Ni active sites for H2 dissociation. Second, the surface oxygen vacancies formed on CeO2 facilitate CO2 activation. Therefore, the best performance of 63% CO2 conversion and 99% CH4 selectivity at 250 °C is achieved on the Ni-5Ce catalyst with small Ni particles and optimal amount of CeO2 promoter. With higher CeO2 content, Ni-7.5Ce catalyst displays decreased catalyst reducibility and catalytic activity. Therefore, it can be concluded that a proper ratio between both types of sites is crucial for CO2 methanation.

Development of Mo-Modified Pseudoboehmite Supported Ni Catalysts for Efficient Hydrogen Production from Formic Acid.

Formic acid (FA), as a safe and renewable liquid hydrogen storage material, has attracted extensive attention. In this paper, a series of Mo-modified pseudoboehmite supported Ni catalysts were developed and evaluated for efficient hydrogen production from formic acid. Pseudoboehmite (PB) as a catalyst carrier was used for the first time. Ni/PB and NiMo/PB possessed a mesostructure, and the pore size distribution was mainly concentrated between 2 and 20 nm. The oxygen vacancies caused by Mo enhanced Ni anchoring, thus inhibiting Ni sintering. Compared with Ni10/PB (7.62 nm), Ni10Mo1/PB had smaller Ni particles (5.08 nm). The Ni–O–Al solid solutions formed through the interaction of Ni with the PB improved the catalytic performance. Ni10Mo1/PB gave the highest conversion of 92.8% with a H2 selectivity of 98% at 300 °C, and the catalyst activity hardly decreased during the 50 h stability test. In short, Ni10Mo1/PB was a promising catalyst for hydrogen production from formic acid because of the oxygen vacancy anchoring effect as well as the formation of Ni–O–Al solid solutions which could effectively suppress the Ni sintering.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

High-efficiency catalytic hydrodeoxygenation of lignin-derived vanillin with nickel-supported metal phosphate catalysts

Lignin is a natural and renewable aromatic raw material of aromatic chemicals and its depolymerization and downstream products conversion has drawn considerable attention. Herein, a series of Ni loaded metal phosphates (Ni/MP, M = Ti, Zr, Nb, La, or Ce) catalysts were fabricated for the hydrodeoxygenation (HDO) of lignin-derived vanillin (VAN) to produce 2-methoxy-4-methylphenol (MMP). It has been demonstrated that 97.25% VAN conversion could be obtained with a yield of 88.39% of MMP under the mild condition of 220 °C and 0.5 MPa H2 for 30 min with 15 wt% Ni/ZrP. The highest activity of Ni/ZrP was attributed to its small Ni particle size, large specific surface area, strong metal-support interaction, and optimal acidity. It has been proven that Ni, Lewis acid sites (LAS) and Brønsted acid sites (BAS) have a synergistic effect in VAN conversion: Nano-sized Ni catalyze the dissociation of H2 to form active hydrogen species (H). LAS promote the adsorption and activation of VAN and isopropanol. BAS play a vital role in the dehydration reaction. Additionally, H2 was the primary hydrogen donor in the system, while isopropanol was the reaction medium as well as the secondary hydrogen donor, helping to reduce the external H2 supply requirement. By optimizing the reaction conditions and studying the promotion mechanism, we hope to provide an experimental basis for lignin catalytic hydrogenolysis.

Ni-CeO2 Catalyst with High Ni Loading Prepared by Salt-Assisted Solution Combustion for CO2 Methanation

An Ni-CeO2 catalyst with high Ni loading (50 wt.%) prepared by a salt-assisted solution combustion method was characterized by different methods and used for CO2 methanation. The specific surface area of the Ni-CeO2 catalyst prepared by salt-assisted solution combustion is 7 times that of the catalyst prepared by conventional solution combustion. The Ni-CeO2 catalyst prepared by salt-assisted solution combustion has smaller particle sizes of Ni and exhibits excellent activity at low temperatures. The high Ni loading and small Ni particle size can provide more metal Ni site and Ni-CeO2 interface, which help to improve the CO2 methanation performance.

Study on the promotional effect of lanthana addition on the performance of hydroxyapatite-supported Ni catalysts for the CO2 methanation reaction

The performance of nickel supported on lanthana-modified hydroxyapatite (HAP) catalysts is investigated in the CO2 methanation. The addition of La (1–6.6 wt%) leads to a surface enrichment following a sequential multilayer deposition model. Moreover, La addition systematically improves the dispersion of Ni particles and their reducibility, which in turn increases spectacularly the amounts of basic sites and their thermal stability. Such physicochemical changes impact positively on the activity of the catalysts in CO2 methanation. The estimated turnover frequency (TOF) suggest that the small Ni particles are the most efficient. The latter seem to provide a large density of very active defects on Ni-La2O3 interface. The optimized catalyst proves to be highly resistant to deactivation during 100 h time-on-stream (TOS). The samples were also assayed as dual function materials (DFMs) for CO2 adsorption and methanation. A scheme is proposed to describe the different steps involved in a CO2 adsorption/hydrogenation cycle.

Influence of Catalyst Reduction Temperature on Autogenous Glycerol Hydrogenolysis over NiAl Catalyst

AbstractAutogenous glycerol hydrogenolysis to 1,2‐propanediol by aqueous phase reforming (APR) was investigated over supported nickel catalysts. Effect of reduction temperature on physico‐chemical properties of catalysts played a significant role in tuning conversion and product selectivities. The formation of nickel aluminate (NiAl2O4) spinel phase during catalyst reduction led to rearrangement of Ni species to obtain small and stable Ni particles. The catalyst activation temperature alters the extent of reduction of multivalent Ni species (Ni0, Ni+2/+3) which facilitated glycerol dehydration and hydrogenation while suppressing C−C cleavage and thus avoiding undesirable side products. Additionally, presence of moderate BrØnsted/Lewis acid ratio of the catalyst promoted higher 1,2‐PDO selectivity. In‐situ glycerol hydrogenolysis involves glycerol dehydration to acetol with simultaneous reforming to H2 and CO2 and this hydrogen converts acetol to 1,2‐PDO.