ZrO2 Support Research Articles

Catalytic valorization of glycerol in the absence of external hydrogen: Effect of the Cu/ZrO2 catalyst mass and solvent

The glycerol valorization by heterogeneous catalysis to produce high-value-added chemicals is mainly carried out in the presence of high pressures of molecular hydrogen, a highly flammable gas whose main production in our days depends on fossil fuels. Therefore, an attractive alternative to explore is hydrogen in-situ generation in the catalytic process. Herein, we investigated the liquid-phase catalytic valorization of 80% wt. glycerol in different solvents such as water, 2-propanol, and acetone using a Cu/ZrO2 catalyst in the absence of external hydrogen. Firstly, the mass effect of the Cu/ZrO2 in the glycerol aqueous medium was evaluated finding an optimum mass of 250 mg for glycerol conversion. At these conditions, an initial reaction rate value of 2.63 × 10−3 molgly·gcat−1·min−1 was observed while the main products were hydroxyacetone (HA) and 1,2-propanediol (1,2-PDO). The use of 2-propanol as solvent and hydrogen donor molecule in the glycerol conversion induced the hydrogenation of hydroxyacetone towards 1,2-PDO. The ratio between the selectivity of 1,2-PDO/HA was found to be higher than that observed for the catalytic experiment with water. For the conversion of glycerol in the presence of acetone as a solvent it was noted the occurrence of acetalization reaction of glycerol with acetone and the main product observed was 4-hydroxymethyl-2,2-dimethyl-1,3-dioxalane or solketal. Density functional theory (DFT) calculations were included to gain insight into the reaction mechanisms of the hydroxyacetone hydrogenation to the formation of 1,2-PDO on Cu/ZrO2 catalyst. Four possible pathways were considered. The elementary steps include several intramolecular hydrogen atom transfer steps and two hydrogen addition steps. The hydrogen sources would come from adsorbed hydroxyl species of the aqueous reaction medium on ZrO2 support.

Activity competition of catalysts and supports materials on the growth of carbon nanotubes with ZrO2/Fe catalyst

Activity competition commonly exist when using multiple catalyst particles for growing carbon nanotubes (CNTs), and the diverse catalysts can compete with the carbon source and affect the growth kinetics and morphology of the nanotubes. However, the existed problem is that whether the support materials themselves also can engage in activity competition with the catalysts, and how this may impact the growth of CNTs. Here, we investigated the influence of hypoactive ZrO2 support material and hyperactive ZrO2/Fe catalysts on the growth of CNTs, and the activity competition relationship between the support and the catalysts. ZrO2/Fe catalysts were prepared via a facile hydrothermal method, and employed both CH4 and C2H5OH as carbon sources for growing CNTs. It is interesting that single-walled carbon nanotubes (SWCNTs) were grown by utilizing CH4 as carbon source, and multi-walled carbon nanotubes (MWCNTs) were synthesized for the use of C2H5OH as carbon source. A combination of experimental data and density functional theory simulations was able to reveal the underlying activity competition mechanism between hyperactive catalysts and hypoactive supports. It would provide new insight into the growth mechanisms of CNTs, and provide new ideas for the rational design and controlled growth of CNTs.

Crucial Role of Surface FeOx Components on Supported Fe-Based Nanocatalysts for CO2 Hydrogenation to Light Olefins

Currently, Fe-based catalysts show excellent catalytic performance in the hydrogenation of CO2 to produce light olefins. Despite numerous studies, the identification of the role of catalytically active components over Fe-based catalysts for CO2 hydrogenation is not quite clear. In this work, a series of ZrO2-supported cobalt-doped Fe-based catalysts were fabricated by a microliquid film reactor-assisted coprecipitation method. It was demonstrated that appropriately strong interactions between Fe-containing species and the ZrO2 support in catalyst precursors could facilitate the generation of a defective FeOx component upon reduction treatment and inhibit the carburization of metallic iron during the reaction. Among all Fe-based catalysts, the catalyst bearing a (Co + Fe)/ZrO2 mass ratio of 3:7 and a Co/Fe molar ratio of 1:9 achieved a highest light olefins selectivity of about 38% at 49% CO2 conversion under reaction conditions (i.e., 320 °C, 2.0 MPa, and 4800 mL·gcat–1·h–1), along with a high Fe time yield to light olefins of 9.2 μmolCO2·gFe–1·s–1 and a low CO selectivity of 4.7%. Comprehensive structural characterization and catalytic CO2 hydrogenation experiments clarified that the surface-dominant defect-rich FeOx component as catalytically active species substantially played a crucial role in governing the hydrogenation of CO2, mainly owing to their enhanced adsorption and binding ability for CO2 and the CO intermediate. This study offers a new strategy to design Fe-based catalysts and provides deep insight into the role of iron oxide species for CO2 hydrogenation to produce light olefins.

Critical role of support crystal structures on highly selective hydrodeoxygenation of lignin-derived vanillin over Pd/ZrO2 catalysts

Hydrodeoxygenation (HDO) of bio-oils obtained by rapid pyrolysis of biomass into high value-added chemicals generally required harsh conditions. Herein, three kinds of mixed-phase ZrO2 supports (denoted as ZSX, X = 2–4) with different crystal structure proportions were prepared by one-pot hydrothermal synthesis method, and their performance on the properties of Pd/ZrO2 catalysts were investigated for vanillin HDO. Pd/ZS3 exhibited excellent efficiency in HDO of vanillin, a typical model compound of lignin, achieving approximately 100% yield of 2-methoxy-4-methylphenol (MMP) in presence of n-butanol as solvent and polymethyl hydrogen siloxane (PMHS) as hydrogen donor under mild conditions (35 °C, 1 h). It was due to catalytic synergy of exposed metal active sites, oxygen vacancies (Ov) and acid sites to occur electron transfer and enhance interaction between Pd and ZrO2. By tuning the crystal structure of ZrO2 support, the influence of Ov and acid sites of Pd/ZrO2 over vanillin HDO performance was investigated, Pd/ZS2 with abundant Ov and Pd/ZS4 with substantial acid sites promoted hydrogenation and hydrogenolysis, respectively, Pd/ZS3 possessed preferable conversion and selectivity as having the properties of both at once. Additionally, reaction pathway was also proposed in which vanillin was converted to MMP by combining intermediate of 4-hydroxy-methyl-2-methoxyphenol (HMP) with active hydrogen species while removing water. This developed catalysts with different crystalline highlighted an enormous promise for HDO of bio-oils into green fuel under mild conditions.

Imaging Interface and Particle Size Effects by In Situ Correlative Microscopy of a Catalytic Reaction.

The catalytic behavior of Rh particles supported by three different materials (Rh, Au, and ZrO2) in H2 oxidation has been studied in situ by correlative photoemission electron microscopy (PEEM) and scanning photoemission electron microscopy (SPEM). Kinetic transitions between the inactive and active steady states were monitored, and self-sustaining oscillations on supported Rh particles were observed. Catalytic performance differed depending on the support and Rh particle size. Oscillations varied from particle size-independent (Rh/Rh) via size-dependent (Rh/ZrO2) to fully inhibited (Rh/Au). For Rh/Au, the formation of a surface alloy induced such effects, whereas for Rh/ZrO2, the formation of substoichiometric Zr oxides on the Rh surface, enhanced oxygen bonding, Rh-oxidation, and hydrogen spillover onto the ZrO2 support were held responsible. The experimental observations were complemented by micro-kinetic simulations, based on variations of hydrogen adsorption and oxygen binding. The results demonstrate how correlative in situ surface microscopy enables linking of the local structure, composition, and catalytic performance.

Deciphering the ZrO2 phase engineering effects on dry reforming of methane over the Ni/ZrO2 catalysts

The Ni/ZrO2 catalyst, with inexpensive price, high activity and excellent thermostability, has been widely investigated for dry reforming of methane (DRM). However, the stability of the catalyst still remains challenging due to the inevitable Ni sintering and carbon deposition under the high-temperature operation. Herein, the effects of the ZrO2 phase engineering in the Ni/ZrO2 catalyst on the DRM performance are highlighted. The characterization results reveal that the rising precipitated temperature can improve the tetragonal ratio (vt) in the catalysts using KOH as the precipitant and the catalyst with higher vt can be obtained via employing Na2CO3 or NaOH as the precipitant. The increased vt might be caused by the increased Ni content inserted into the ZrO2 support lattice. Ni dispersion is promoted with the raised vt resulting from the enhanced metal-support interaction. Besides, stronger acidity-basicity and more defects, including Zr3+ and surface oxygen species, are also detected on the catalyst with higher vt. Thus, the activity and stability over the Ni/ZrO2 catalysts displays a positive relation with the vt value. Especially, the conversions of CH4 and CO2 over the catalyst precipitated at 80 °C with NaOH as the precipitant are 80% ∼ 62% and 85% ∼ 72%, respectively, after evaluated for 3600 min with 4.3% carbon deposition. It has also been identified that the tetragonal ZrO2 plays a vital role in restraining carbon accumulation and graphitization. Furthermore, the infrared spectroscopy experiments illustrate that the reactive oxygen species are richer on the catalyst with higher vt and easier to react with CH4.

Theoretical insights into the support effect on the NO activation over platinum-group metal catalysts.

We systematically explored NO activation at metal/oxide interfaces by the combination of Sr3Ti2O7, Sr3Fe2O7, CeO2, anatase-TiO2, ZrO2, and γ-Al2O3 supports and the platinum-group metal cluster (Pd4, Pt4, and Rh4) using slab-model density functional theory calculations. These metal clusters can be strongly adsorbed at these metal oxide surfaces. The Pt4 and Rh4 clusters show larger adsorption energies than the Pd4 cluster, yet the γ-Al2O3(100) surface shows smaller adsorption energies than other metal oxide surfaces. One oxygen vacancy close to the metal cluster was constructed to evaluate the NO activation at those metal/oxide interfaces. The O atom of NO refills the oxygen vacancy after NO dissociation, while the N adatom is left on the metal cluster. The exothermic process was identified for the NO activation except for the Sr3Fe2O7 case, indicating the significant role of the interplay between the metal cluster and oxygen vacancy.

Direct ethyl acetate synthesis from ethanol over amorphous-, monoclinic-, tetragonal ZrO2 supported copper catalysts prepared from the same zirconium source

Direct ethyl acetate synthesis from ethanol was examined by supported Cu catalysts on various kinds of acid-base metal oxides, available ZrO2-based oxides, and homemade amorphous-, monoclinic- and tetragonal zirconia prepared from the same Zr source. XRD, XAFS, TG-DTA characterization and surface area measurement were performed. Effects of crystalline phase of ZrO2 support on selective ethyl acetate production was discussed based on the yields and products ratio (ethyl acetate to sum of C4-alcohols and aldehydes). Based on catalytic performance by 29 kinds of homemade catalysts, amorphous-type ZrO2 was found to be essentially the most suitable ZrO2 phase for the selective ethyl acetate formation in cases without any surface modifications. The acid site on the surface of monoclinic-type ZrO2 catalysts possibly promoted unfavorable acetaldehyde condensation reaction, but addition of Na+ for poisoning could increase selectivity of ethyl acetate formation. Coordination environment of Cu species for fresh and spent catalysts were discussed.

Multifunctional WO3-ZrO2-Supported Platinum Catalyst for Remarkably Efficient Hydrogenolysis of Esters to Alkanes.

The hydrogenolysis of esters to alkanes is a key protocol for the synthesis of high-quality hydrocarbon fuels from renewable plant oils or fats. However, performing this process under mild energy-efficient conditions is challenging. Herein, we report a robust tungsten- and zirconium-oxide-supported platinum catalyst (Pt/WO3-ZrO2) for the hydrogenolysis of esters to alkanes at low temperatures (as low as 70 °C) and under ambient pressure (1 atm) of H2. For example, tristearin undergoes a complete conversion at 130 °C with more than 95% selectivity for the corresponding alkanes without carbon loss. In addition, the heterogeneous nature of the catalyst system reported herein permits multiple reuse of the catalyst without any significant loss of its high activity and selectivity. Mechanistic studies suggest that the multifunctional nature (acid and redox properties) of the WO3-ZrO2 support plays an important role in the high activity of the catalyst.

Probing the Nature of Zinc in Copper-Zinc-Zirconium Catalysts by Operando Spectroscopies for CO2 Hydrogenation to Methanol.

Active Zn species in Cu-based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO2 support is established in Cu-based catalysts by separating Zn and Zr components from Cu (Cu-ZnZr) via the double-nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with Cu-ZnO interface and isolated ZnO nanoparticles. Operando X-ray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened Zn-Zr interaction. They can suppress formate decomposition to CO and decrease the H2 dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi-component catalysts.

Probing the Nature of Zinc in Copper‐Zinc‐Zirconium Catalysts by Operando Spectroscopies for CO2 Hydrogenation to Methanol

AbstractActive Zn species in Cu‐based methanol synthesis catalysts have not been clearly identified yet due to their complex nature and dynamic structural changes during reactions. Herein, atomically dispersed Zn on ZrO2 support is established in Cu‐based catalysts by separating Zn and Zr components from Cu (Cu−ZnZr) via the double‐nozzle flame spray pyrolysis (DFSP) method. It exhibits superiority in methanol selectivity and yield compared to those with Cu−ZnO interface and isolated ZnO nanoparticles. Operando X‐ray absorption spectroscopy (XAS) reveals that the atomically dispersed Zn species are induced during the reaction due to the strengthened Zn−Zr interaction. They can suppress formate decomposition to CO and decrease the H2 dissociation energy, shifting the reaction to methanol production. This work enlightens the rational design of unique Zn species by regulating coordination environments and offers a new perspective for exploring complex interactions in multi‐component catalysts.

Steering ammonia decomposition over Ru nanoparticles on ZrO2 by enhancing metal–support interaction

Enhanced metal–support interaction between Ru nanoparticles and ZrO2 support can steer the catalytic activity of the supported Ru nanoparticles for the production of hydrogen from ammonia decomposition.

Advancing nitrate reduction to ammonia: insights into mechanism, activity control, and catalyst design over Pt nanoparticle-based ZrO2.

The reduction of nitrogen oxides (NOx) to NH3, or N2 represents a crucial step in mitigating atmospheric NO3 and NO2 emissions, a significant contributor to air pollution. Among these reduction products, ammonia (NH3) holds particular significance due to its utility in nitrogen-based fertilizers and its versatile applications in various industrial processes. Platinum-based catalysts have exhibited promise in enhancing the rate and selectivity of these reduction reactions. In this study, we employ density functional theory (DFT) calculations to explore the catalytic potential of Pt nanoparticle (PtNP)-supported ZrO2 for the conversion of NO3 to NH3. The most favorable pathway for the NO3 reduction to NH3 follows a sequence, that is, NO3 → NO2 → NO → ONH → ONH2/HNOH → NH2/NH → NH2 → NH3, culminating in the production of valuable ammonia. The introduction of low-state Fe and Co dopants into the ZrO2 support reduces energy barriers for the most challenging rate-determining hydrogenation step in NOx reduction to NH3, demonstrating significant improvements in catalytic activity. The incorporation of dopants into the ZrO2 support results in a depletion of electron density within the Pt cocatalyst resulting in enhanced hydrogen transfer efficiency during the hydrogenation process. This study aims to provide insights into the catalytic activity of platinum-based ZrO2 catalysts and will help design new high-performance catalysts for the reduction of atmospheric pollutants and for energy applications.

Ni-catalyzed CO2 glycerol reforming to syngas: New insights on the evaluation of reaction and catalyst performance

Glycerol dry reforming (GDR) to syngas was studied on Ni/ZrO2, Ni/La2O3 and Ni/La2O3–ZrO2 catalysts for elucidating the effects of support material on catalyst performance. A methodology was proposed to quantify the produced H2O, which was not reported so far in the GDR literature. At 750 °C, molar inlet CO2–to–glycerol vapor ratio (CO2/G) of 1–3 and residence time of 0.25 mgcat.min/Nml, the average CO2 and glycerol conversions were ordered as 13 % (NiLZ) > 10 % (NiZ) > 9 % (NiL) and 93 % (NiLZ) > 89 % (NiZ) > 83 % (NiL), respectively. NiLZ, the most active catalyst, also delivered > 95 % of the pertinent thermodynamic CO2 conversion at 0.5 mgcat.min/Nml. The 24 h stability of NiL and NiZ catalysts depended strongly on the inlet CO2 concentration. At CO2/G = 2, NiL deactivated by ∼5 % which was doubled at CO2/G = 4 mainly due to coking shown by TGA and Raman spectroscopy. The catalyst also suffered from Ni agglomeration as revealed by SEM–EDX and XRD. NiZ catalyst lost ∼21 and ∼9 % of its initial activity after 24 h aging at CO2/G = 2 and 4, respectively. Despite insignificant coking and sintering, XPS analyses pointed out almost four–fold decrease in the surface atomic Ni concentration on NiZ at CO2/G = 2 and suggested partial blockage of Ni sites by increased reducibility of monoclinic ZrO2 support at the less oxidative, CO2–lean environment. Regardless of the atmosphere, the NiLZ catalyst showed excellent stability features comparable to those of the notably higher–priced Rh and Ru–containing counterparts.

Highly dispersed Pd anchored on heteropolyacid modified ZrO2 for high efficient hydrodeoxygenation of lignin-derivatives

Production of biofuels and value-added chemicals from renewable biomass is a strategy with great promise to replace petrochemicals. Herein, we developed an efficient method to fabricate highly dispersed Pd anchoring on phosphotungstic acid (PTA)-modified ZrO2. The optimized metal–acid bifunctional catalyst, Pd-PTA/ZrO2, displayed excellent catalytic performance for the hydrodeoxygenation of lignin-derivatives under mild conditions. High conversion of vanillin and high selectivity of 2-methoxy-4-methylphenol can be achieved at 80 °C for 90 min under 1 atm H2, which overcame most of the reported catalysts. The outstanding catalytic activity can be attributed to the large surface area, moderate acid strength, the synergetic effect of the active metal and ZrO2 support. This study provides a feasible route to prepare highly dispersed catalysts with superior catalytic performance for bio-fuel upgrading.

Zirconium Carbide Mediates Coke-Resistant Methane Dry Reforming on Nickel-Zirconium Catalysts.

Graphitic deposits anti-segregate into Ni0 nanoparticles to provide restored CH4 adsorption sites and near-surface/dissolved C atoms, which migrate to the Ni0 /ZrO2 interface and induce local Zrx Cy formation. The resulting oxygen-deficient carbidic phase boundary sites assist in the kinetically enhanced CO2 activation toward CO(g). This interface carbide mechanism allows for enhanced spillover of carbon to the ZrO2 support, and represents an alternative catalyst regeneration pathway with respect to the reverse oxygen spillover on Ni-CeZrx Oy catalysts. It is therefore rather likely on supports with limited oxygen storage/exchange kinetics but significant carbothermal reducibility.

A highly efficient Cu/ZnOx/ZrO2 catalyst for selective CO2 hydrogenation to methanol

The ternary Cu/ZnO/Al2O3 catalyst is usually employed for producing methanol from syngas (CO/CO2/H2) or from CO2 hydrogenation in industry. However, this catalyst often suffers from the aggregation of Cu nanoparticles and the phase separation of Cu and ZnO. In this work, a highly efficient and stable catalyst (Cu/ZnOx/ZrO2) for CO2 hydrogenation to methanol is prepared via co-precipitation method with UiO-66 as structural template. Cu/Zn is effectively combined and encapsulated in the channels of UiO-66, which avoids the aggregation of metal particles. The ZrO2 support derived from UiO-66 enhances the interaction between the support and Cu/Zn, and thus improves the catalytic performance significantly. This catalyst shows a high space–time yield of 216.7 g(MeOH)·kg(cat)−1·h−1 at 260 °C, 4 MPa and GHSV = 12000 h−1. Furthermore, the catalyst shows good stability over a period of 50 h on stream. The performance of Cu/ZnOx/ZrO2 is much better than that of commercial catalysts and most of catalysts previously reported.

Role of ZrO2 and CeO2 support on the In2O3 catalyst activity for CO2 hydrogenation

Methanol synthesis from CO2 hydrogenation has drawn global attention as catalytic CO2 hydrogenation is an attractive choice to mitigate CO2 emissions and lessen dependency on fossil resources. In the present study, we have synthesized ZrO2 and CeO2-supported In2O3 catalysts for methanol synthesis from CO2 hydrogenation and the catalytic performances of Inx/ZrO2, and Inx/CeO2 (x = 1 % and 13 %) were compared. Specifically, the effect of the ZrO2 and CeO2 supports on In2O3 catalyst during CO2 hydrogenation was explored. This study reveals that ZrO2 support increased the catalytic activity while the CeO2 support decreased although both supports have almost the same indium loading and surface area. Various characterizations like XRD, DRIFT, CO2-TPD, H2-TPR and XPS analysis of catalysts provided insight into changes that arise after mixing the two oxides and during the reaction as well as after the reaction. The stabilities of In2O3, In13/ZrO2, and In13/CeO2 were tested for up to 50 h and we found In13/ZrO2 was stable during this time-on-stream, while In13/CeO2 lost activity after 2 h of reaction. XPS results of spent catalysts showed that In(OH)3 was observed significantly over the spent In13/CeO2. OH groups were also verified by DRIFT experiments, however at low levels due to low CO2 conversion at atmospheric pressure. XRD analysis confirmed the sintering of CeO2 support during the reaction. Thus, the hydrophilic nature of CeO2, redox properties of CeO2 and sintering of CeO2 support in the presence of water, were the main reasons for the early deactivation of In13/CeO2. A regeneration study was carried out to regenerate the catalyst and the results showed that partial regeneration of the In13/CeO2 catalyst is possible by Ar flushing. We, therefore, suggest that the build-up of OHgroups deactivate the In13/CeO2 catalyst and some of these OH groups could be removed during flushing with inert gas, causing a partial regeneration. However, the decreased surface area is not reversible, and this results in a continuous decrease in the activity of the catalyst after repeated experiments, even if the catalyst is flushed with Ar between the experiments.

Interfacial dependent reactive oxygen species generation over Pt-ZrO2 nanoparticles for catalytic oxidation of formaldehyde at room temperature

Producing the strong metal-support interaction (SMSI) interface and highly reactive oxygen species is a great challenge for catalytic oxidation of formaldehyde (HCHO) at room temperature over supported metal catalysts. Herein, we report a conceptual oxygen vacancy (VO) associated SMSI interface of Pt-ZrO2 nanoparticles for HCHO catalysis at room temperature, exhibiting interfacial dependent reactive oxygen species (O*) formation. The VO on the ZrO2 support captures and activates the molecular O2, then proceeds to generating the reactive oxygen atom (O*) with a lower activation barrier of 0.3 eV. The generated O* tends to link the (110) surface of ZrO2 and the (111) surface of Pt as an electronic transmission channel for the selective catalytic oxidation of HCHO adsorbed on the (110) surface of ZrO2, accelerating the direct generation of formate species and mineralization of HCHO. The Pt-VO-ZrO2 achieves high HCHO removal and HCHO conversion (>95%) at 20 °C. These findings will consolidate the fundamental theories of room temperature catalytic reactions via constructing the SMSI interface engineering for wide environmental applications.

Barium-Promoted Yttria-Zirconia-Supported Ni Catalyst for Hydrogen Production via the Dry Reforming of Methane: Role of Barium in the Phase Stabilization of Cubic ZrO2.

Developing cost-effective nonprecious active metal-based catalysts for syngas (H2/CO) production via the dry reforming of methane (DRM) for industrial applications has remained a challenge. Herein, we utilized a facile and scalable mechanochemical method to develop Ba-promoted (1–5 wt %) zirconia and yttria–zirconia-supported Ni-based DRM catalysts. BET surface area and porosity measurements, infrared, ultraviolet–visible, and Raman spectroscopy, transmission electron microscopy, and temperature-programmed cyclic (reduction–oxidation–reduction) experiments were performed to characterize and elucidate the catalytic performance of the synthesized materials. Among different catalysts tested, the inferior catalytic performance of 5Ni/Zr was attributed to the unstable monoclinic ZrO2 support and weakly interacting NiO species whereas the 5Ni/YZr system performed better because of the stable cubic ZrO2 phase and stronger metal–support interaction. It is established that the addition of Ba to the catalysts improves the oxygen-endowing capacity and stabilization of the cubic ZrO2 and BaZrO3 phases. Among the Ba-promoted catalysts, owing to the optimal active metal particle size and excess ionic CO32– species, the 5Ni4Ba/YZr catalyst demonstrated a high, stable H2 yield (i.e., 79% with a 0.94 H2/CO ratio) for up to 7 h of time on stream. The 5Ni4Ba/YZr catalyst had the highest H2 formation rate, 1.14 mol g–1 h–1 and lowest apparent activation energy, 20.07 kJ/mol, among all zirconia-supported Ni catalyst systems.