Hydroxyapatite Catalysts Research Articles

Effect of cobalt on the activity of nickel-based/magnesium-substituted hydroxyapatite catalysts for dry reforming of methane

The dry reforming of methane (DRM) reaction can directly convert methane (CH4) and carbon dioxide (CO2) into syngas (H2+CO), which is a promising method for achieving carbon neutralization. In this study, a series of 3Ni-xCo/Mg1HAP alloy catalysts with different ratios were synthesized by the coprecipitation method, and the optimum Ni/Co ratio for the DRM reaction was studied. A series of characterization methods revealed that after Co was added, the formation of Ni–Co alloys increased the interactions between metals. However, an excess of Co inhibits the entry of Ni into the lattice of Mg1HAP, resulting in metal accumulation on the surface of the support. In addition, the introduction of Co improves the dispersion of Ni metal, which endows the catalyst with better catalytic activity and stability. Raman spectroscopy of the catalyst after the stability test showed that the addition of Co reduced the proportion of graphitic carbon, which was also the main reason for its improved stability.

Adsorption mechanisms, kinetics and photoactivities of green synthesized hydroxyapatite supported ZnO and La–ZnO catalysts

In this study, hydroxyapatite (HAP) is synthesized by a co-precipitation method from the waste eggshell, utilized as a support for ZnO (ZnO-HAP) and La–ZnO (La–ZnO-HAP) and employed to degrade methyl orange (MO) and methylene blue (MB) dyes under UV irradiation. Water vapor adsorption as relative humidity (84 % RH) on the HAP structure and the as-prepared catalysts are also examined. The characteristic ZnO and HAP reflections are detected in X-ray diffraction (XRD) analysis of ZnO-HAP, La–ZnO-HAP and humidified samples. ZnO and La–ZnO existence is also verified by scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, UV–Vis diffuse reflectance (UV–Vis DRS) spectra and X-ray photoelectron spectra (XPS). ZnO and La–ZnO loading on the HAP induce the formation of mesoporous structures with high surface areas. Dark adsorption capacities and photoactivities of the as-prepared samples are explored regarding electrostatic interactions, Lewis acid-base interactions and hydrogen bonding for both MO and MB. In particular, La–ZnO-HAP 500 °C and La–ZnO-HAP 500 °C (RH) exhibit improved adsorption abilities and photoactivities. The pseudo-second order model describes the kinetic behavior of all samples under dark conditions. Unhumidified samples follow Langmuir isotherm while Freundlich isotherm better fits humidified ones. Under irradiation, the Langmuir-Hinshelwood kinetic model describes the photoactivities of all samples. The four recycling tests confirm the stabilities of HAP 100 °C, HAP 500 °C, ZnO-HAP 500 °C and La–ZnO-HAP 500 °C. This study suggests that the ZnO or La–ZnO loaded HAP catalysts prepared in the presence and absence of humid conditions are considered promising materials for environmental remediation.

A Novel Ru Loaded Hydroxyapatite Catalyst Prepared by a Facile and Efficient Deposition Method for Catalytic Oxidation of Toluene and Dichloromethane

A Novel Ru Loaded Hydroxyapatite Catalyst Prepared by a Facile and Efficient Deposition Method for Catalytic Oxidation of Toluene and Dichloromethane

Copper-supported hydroxyapatite catalysts for bio-isobutanol synthesis from sustainable short-chain alcohols

Developing high-performance catalysts for the direct production of isobutanol through the Guerbet reaction is a challenge today, due to the potential of isobutanol as fuel. The present study describes the synthesis and characterization of Cu-supported hydroxyapatite catalysts. The synthesis of isobutanol has been investigated through batch experiments and in a continuous-flow reactor operating in a gas-solid phase. This study used ethanol and methanol as the primary feedstock for the synthesis process. It was found that Cu supported hydroxyapatite catalysts are capable of catalyzing the formation of isobutanol from CH3OH and C2H5OH at temperatures (300–500 ºC) and 1 atm in a continuous flow reactor. Notably, the highest selectivity to isobutanol was observed at 400 ºC. The use of Cu10/HAP 1.65 catalyst in a batch reactor greatly enhances the selectivity of iBuOH in the liquid phase, increasing it from 18 % (vapor-phase) to 65 %. The data showed that the reaction of ethanol/methanol was limited by the 1-propanol-to-isobutanol reaction, which is a secondary reaction of the key intermediate. A reaction scheme has been proposed.

Elimination of synthetic dyes by clamshell derived photo-active hydroxyapatite

Herein, a novel designed hydroxyapatite (HAp) derived from freshly calcined clamshell waste through the wet precipitation method was synthesized. HAp has been developed as a heterogeneous photocatalyst for the anionic dye methyl orange (MO) degradation. The pH on synthesizing HAp was varied in basic conditions. The results show HAp formed at pH more than 10. The MO photodegradation was done under UV-light irradiation for 120 min. HAp catalyst showed the optimum MO degradation efficiency using rod-like structure HAp synthesized at pH 12. HAp with optimum photodegradation efficiency was optimized for the catalyst loading and the pH of the MO solution. MO at pH 6 with 0.05 g catalyst loading showed the highest degradation efficiency around 97 % using HAp prepared at pH 12 with band gap at 4.990 eV. This finding brings a new insight on natural sources materials as photo-active in sustainable of persistent water pollutants.

Surface immobilization mechanisms of cobalt ions on hydroxyapatite catalyst supports

Cobalt deposition in an excess of solution was used to design Co-modified hydroxyapatite materials with various Co loadings and controlled dispersion. It is rationalized how the properties of hydroxyapatite supports (more or less stoichiometric compositions, nanorod or platelet morphologies and crystalline (100) zig-zag termination or non-apatitic hydrated external layer), influence the immobilization processes of Co by operating either with slightly acidic (natural) or basic pH of the suspension media. Four cobalt immobilization mechanisms impacting the final dispersion of Co on hydroxyapatites were identified by combining structural (XRD, 1H and 31P solid-state NMR, UV-Vis, Raman and X-ray fluorescence spectroscopies), surface (XPS) characterizations of Co-modified hydroxyapatites after drying and thermal treatment at 500 °C, and monitoring of the pH and the composition of the supernatant solutions during the Co deposition step. On dried Co-modified crystalline stoichiometric hydroxyapatite nanorods, cobalt is highly dispersed through cationic exchange or strong electrostatic adsorption (SEA) at slightly acidic or basic pH, respectively. After thermal treatment at 500 °C, only cation exchange preserved atomic dispersion of Co(II) ions since Co3O4 nanoparticles were observed on samples for which Co deposition occurred via SEA. On defective hydroxyapatite platelets, cobalt deposited at acidic natural pH could diffuse in an external non-apatitic layer, whereas under basic pH media, this surface layer was hydrolysed, resulting in the formation of a cobalt-substituted hydroxyapatite layer in which only a limited fraction of the surface cobalt species could be probed by XPS.

Hydrogenation of glucose to sorbitol by using nickel hydroxyapatite catalyst

AbstractA series of nickel hydroxyapatite catalysts were synthesized by the co‐precipitation method followed by calcination and reduction. These catalysts were employed for the aqueous phase hydrogenation of glucose to sorbitol. The Ni‐HAP catalyst with comparatively high surface area and acid‐base strength gave high sorbitol selectivity in 1 h. Ni‐HAP‐4 catalyst with moderate Ni (3.5 wt. %) content having smaller and highly dispersed nickel particles gives an excellent yield of sorbitol, 97 % in 1 h. The Ni‐HAP‐4 catalyst works well with other polar protic solvents. Different characterization techniques like XRD, TEM, SEM‐EDS, BET, NH3‐TPD, and CO2‐TPD were employed to analyze the Ni‐HAP‐4 catalyst.

Polarized hydroxyapatite, a ceramic nanocatalyst to convert automotive carbon emissions into ethanol

This paper is aimed to develop ultrananoporous polarized hydroxyapatite (HAp) catalyst and evaluate its performance in transforming CO2 into useable ethanol considering three different scenarios: 1) a batch reaction using a mixture of CO2 and CH4 as feeding gas; 2) a batch reaction using as reactant exhaust gases captured from the fumes of diesel vehicles; and 3) a continuous flow reaction using pure CO2 as feeding gas. Ultrananoporous HAp scaffolds were prepared using a four-step process: 1) as prepared HAp powder was mixed with 60% wt. of a commercial hydrogel at low-temperature; 2) the resulting paste was shaped at low temperature to reduce the adhesion between the metallic tools and the mixture, enhancing the homogeneity of the sample; 3) the shaped paste was calcined in air by applying 1000 ºC during 2 h to eliminate the hydrogel; and 4) an external DC electric field of 3 kV/cm was imposed at 1000 ºC during 1 h to the calcined scaffold. The resulting polarized scaffolds both ultrananoporosity and catalytic activation. Thus, the mass: volume ratio of the ultrananoporous catalyst was much lower than that of conventional HAp catalyst (718 vs 5093 g/L. Furthermore, the ethanol yield was much higher (up to a factor of ×21.4) for the ultrananoporous catalyst than for the compact one, allowing us to conclude that ultrananoporous polarized HAp catalyst is a promising technology for transforming CO2 into valuable chemical products from highly polluted gases, especially those coming from road, sea and air transport.

Hydroxyapatite supported molybdenum oxide catalyst for selective dehydrogenation of cyclohexane to cyclohexene: studies of dispersibility and chemical environment.

The selective oxidative dehydrogenation of cyclohexane to cyclohexene was conducted using molybdenum oxide (MoO x ) as a catalyst and hydroxyapatite (HAP) and Ca5(OH)(PO4)3 as carriers. Two series of MO x /HAP catalysts with varying MoO x loading capacity and calcination temperature were prepared via the co-impregnation method. The impact of dispersibility and chemical environment on the catalytic performance of MoO x was investigated. The catalysts were characterized using XRD, XPS, H2-TPR, and UV-Vis spectra. These MoO x /HAP catalysts were employed for the oxidative dehydrogenation (ODH) of cyclohexane to cyclohexene. MoO x /HAP catalysts with lower loading capacity exhibited higher dispersion of MoO x and selectivity towards cyclohexane. The calcination temperature directly influenced the chemical environment of MoO x , thereby affecting its catalytic performance. Samples calcinated at lower temperatures (500 °C and 600 °C) demonstrated higher conversion rates for cyclohexane, while samples calcinated at higher temperatures (above 700 °C) displayed greater selectivity towards cyclohexane. At 430 °C, when the conversion rate of cyclohexane reached 13.1%, the selectivity of cyclohexene over MHAP-0.05-800 catalyst reached 58.2%.

Multicomponent synthesis via acceptorless alcohol dehydrogenation: an easy access to tri-substituted pyridines.

Herein, we report palladium supported on a hydroxyapatite catalyst for synthesizing tri-substituted pyridines using ammonium acetate as the nitrogen source via acceptorless alcohol dehydrogenation strategy. The strategy offers a broad substrate scope using inexpensive and readily available alcohols as the starting material. The catalyst was prepared using a simple method and analyzed by several techniques, including FE-SEM, EDS, HR-TEM, BET, XRD, FT-IR, UV-visible spectroscopy, and XPS, demonstrating the anchoring of Pd nanoparticles on hydroxyapatite in the zero oxidation state. Moreover, several controlled experiments were carried out to understand the reaction pathway and a suitable mechanism has been proposed.

Advancing biodiesel production from Pyrus glabra seed oil: Kinetic study and RSM optimization via microwave-assisted transesterification with biocompatible hydroxyapatite catalyst

In this study, a biocompatible hydroxyapatite (HAp) catalyst was synthesized using the chemical precipitation method to create biodiesel (FAME). The HAp was characterized for its structure (FT-IR and XRD), particle size, morphology (SEM and TEM), and surface area (BET). The obtained results indicated that HAp had a spherical shape ranging in size from 28.36 to 51.40 nm, a specific surface area of 21.90 m2/g, and a pore diameter of 15.36 nm. The aforementioned catalyst was employed in the transesterification of Pyrus glabra seed oil, with the assistance of microwaves, and the optimization of the biodiesel production process was achieved using RSM-CCD. The impact of the reaction parameters, including catalyst weight (0.5–1.5 wt%), temperature (60–80 °C), and time (10–30 min), was analyzed. The highest biodiesel yield of 89.21% was achieved in 30 min using a 0.5 wt% catalyst at 80 °C. Microwave-produced FAME was evaluated with FT-IR and GC-MS analysis. GC-MS results revealed 78.02% unsaturated and 13.16% saturated FAME content. The FTIR spectrum validated the presence of methyl and ester groups in the produced biodiesel. Both the FTIR and GC-MS results illustrated that the produced biodiesel had good quality. Transesterification of Pyrus glabra seed Oil followed first-order kinetics with an activation energy of 23.20 kJ/mol and an Arrhenius constant of 2.43 × 104 min−1. The catalyst remained active over six recycling cycles without notable decline. The optimal properties of Pyrus glabra biodiesel, meeting ASTM standards, highlight its potential as a catalyst for large-scale production, aligning with the Sustainable Development Goals (SDGs).

Moroccan sardine scales as a novel and renewable source of heterogeneous catalyst for biodiesel production using palm fatty acid distillate

The continued growth in energy consumption, in concert with the depleting resources of fossil fuels and their detrimental effects on the environment, has required the exploration of substitute, renewable, and sustainable sources of energy. Biodiesel is one such alternative. In this current study, a heterogeneous sulfated catalyst based on Sardine scales was developed to improve biodiesel synthesis from palm fatty acid distillate (PFAD) through esterification. The catalyst was synthesized via a clean flash pyrolysis method with a thermal shock (950 °C) followed by a sulfonation process. The prepared catalyst was characterized by utilizing diverse methods, including XRD, FTIR, TGA/DSC, SEM/EDX, DLS, BET, and the Hammett test. The sulfated hydroxyapatite (HAPSS-SO4) catalyst demonstrated a maximum conversion of PFAD to biodiesel of 96.75% under optimal reaction conditions such as 3 wt% catalyst loading and 15:1 MeOH/PFAD molar ratio for 3 h at 70 °C. Additionally, the catalyst proved excellent stability, with the ability to regenerate for three cycles. The properties of the produced biodiesel are within the limits stipulated by international standards. The results of the molecular simulation demonstrate that the Lewis acid sites (Ca) are very susceptible to attack through the free fatty acid (FFA). The study proved the effectiveness of a sardine scale-derived catalyst (HAPSS-SO4) as a heterogeneous catalyst for biodiesel production.

New performing hydroxyapatite-based catalysts in dry-reforming of methane

Dry reforming of methane (DRM) is a promising process for the production of synthetic gas from carbon dioxide and methane. However, the design of a performing catalyst for this reaction is still challenging since catalyst deactivation usually takes place, principally by thermal sintering at high temperatures (700–950 °C) and by carbon deposition. In this work, calcium hydroxyapatite (HAP) and HAP-doped magnesium (Mg_HAP) supported nickel catalysts were synthesized by wet precipitation method, characterized by various physico-chemical and thermal techniques, and evaluated in DRM reaction. Outstanding catalytic performance in DRM could be obtained with Ni/ HAP and Ni/Mg_HAP catalysts, thanks to a tunable acidity-basicity of these supports, a strong metal-support interaction, and a good thermal stability of nickel nanoparticles. H2 and CO were the main products, with stable selectivity up to 85 ∓ 3%, while H2O and solid carbon were byproducts with 5–10% of selectivity.

Activity of Nickel Supported Over Nanorod-Shaped Strontium Hydroxyapatite Catalysts in Selective Methanation of CO & CO2

Nickel modified strontium hydroxyapatite (Ni/Sr-HAP) supported catalysts are studied in selective methanation of CO/CO2. In this work, a new type of nano rod-shaped strontium hydroxyapatite-based catalysts with two different sizes and aspect ratios were prepared by sol–gel method and in next step, Ni precursor was wet impregnated i.e., denoted as Ni/Sr-HAP and Ni/Sr-HAP(F127). The catalytic tests were performed in CO and CO2 methanation reactions and evaluated the light-off temperatures curves (225–450 °C) under ambient pressure in a fixed-bed flow reactor. The physicochemical properties of the prepared catalysts were characterized by XRD, N2 physisorption, TEM, SEM, TPR, CO2/H2-TPD and H2-chemisorption techniques. From XRD analysis, both Ni/Sr-HAP and Ni/Sr-HAP(F127) were identified as the hydroxyapatite type structure with high crystallinity and very low intensity peaks corresponds to strontium phosphates as the main phase and structure. The TEM and SEM micrographs of Ni/Sr-HAP catalysts displayed a nano- rod shaped morphology with different dimensions and exhibited average Ni particle size of ~ 9.2 nm. While Ni/Sr-HAP(F127) shown the rod size in the length in the range of 100–250 nm and width in the range of 20–40 nm with average Ni particle size 5.7 nm. The F127 mediated support Sr-HAP synthesis i.e., Ni/Sr-HAP(F127) mesoporous catalyst possessed higher metal surface with smaller Ni particles size and possessed higher CO2 adsorption capacity. The medium strength basic sites of Ni/Sr-HAP catalyst played an important role in methanation reactions. Based on the characterization and the catalysts activity results, small sized nanorods of Ni/Sr-HAP(F127) is the most active and selective catalyst due to the higher Ni dispersion, higher amounts of medium basic sites, and reducibility character than the bigger nanorods based Ni/Sr-HAP catalyst.

Imine Oxidation Catalyzed by Zinc Hydroxyapatite: Kinetic Studies

AbstractThe synthesis of N,N‐diphenylformamide from N‐benzylideneaniline and urea hydrogen peroxide is investigated using a zinc hydroxyapatite (ZnHAP) catalyst. It was found that the catalyst resulted in the highest activity of 91 % conversion and 40 % selectivity at 130 °C in 2 h. A kinetic model was validated by Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) at different temperatures and the absence of mass transfer resistance was proved by the Weisz Prater criterion. Effect of different catalysts, catalyst loading, temperature, mole‐ratio, and speed of stirring was studied. The as‐synthesized catalyst is characterized by FTIR, BET nitrogen adsorption‐desorption, TEM, EDX, TPD‐NH3, XPS, ICP‐MS and XRD. ZnHAP catalyst was found to be stable up to three recycles with no loss in activity.

Co-doped hydroxyapatite as photothermal catalyst for selective CO2 hydrogenation

The rational design and in deep understanding of efficient, affordable and stable materials to promote the light-assisted production of fuels and commodity chemicals is very appealing for energy crisis and climate change amelioration. Herein, we have prepared a series of Co-doped hydroxyapatite (HAP) catalysts with different Co content. The materials structure has been widely investigated by XRD, FT-IR, HRTEM, XPS, XAS, as well as computational simulations based on Density Functional Theory (DFT) with PBE functional. At low Co loading, there is a partial substitution of Ca cations in the HAP structure, while higher loadings promote the precipitation of small (∼ 2 nm) Co nanoparticles on the HAP surface. For the optimal Co content, a constant CO rate of 62 mmol·g−1·h−1 at 1 sun illumination and 400 °C, with the material being stable for 90 h. Visible and NIR photons have been determined responsible of the light-assisted activity enhanced. Mechanistic studies based on both experimental and DFT simulations show that H2 preferentially adsorbs to metallic Co, while CO2 adsorbs to the HAP surface oxygen. Moreover, both direct photo- and plasmon-driven contributions have been separated in order to study their mechanisms independently.

Biodiesel production from date seed oil using hydroxyapatite-derived catalyst from waste camel bone

Biodiesel is considered to be more friendly to the environment than petroleum-based fuels, cheaper and capable for producing greener energy which contributed positively in boosting bio-economy. A new non-edible feedstock utilized from date seed oil was analyzed for the synthesis of eco-friendly biodiesel using newly novel hydroxyapatite heterogeneous catalysts, obtaining from waste camel bones prepared from dried camel bone followed calcination under different temperature. This catalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and transmission electron microscopy (TEM). Results showed that hydroxyapatite catalyst pore size reduced with increasing the calcination temperature. Optimize biodiesel yield (89 wt%) was achieved through the process of transesterification with optimum reaction conditions of 4 wt% catalyst, oil to ethanol molar ratio of 1:7 and temperature 75 °C for 3 h reaction time. The production of FAME was confirmed by using gas chromatography-mass spectroscopy (GC–MS). Fuel properties of fatty acid ethyl ester complied with ASTM D 6751 which indicated that it would be an appropriate alternative form of fuel. As a result, using biodiesel made from waste and untamed resources to develop and implement a more sustainable and environmentally friendly energy strategy is commendable. The acceptance and implementation of the green energy method may result in favorable environmental effects, which in turn may lead to better societal and economic growth for biodiesel industry at a larger scale.

Design Strategies for Hydroxyapatite-Based Materials to Enhance Their Catalytic Performance and Applicability.

Hydroxyapatite (HAP) is a green catalyst that has a wide range of applications in catalysis due to its high flexibility and multifunctionality. These properties allow HAP to accommodate a large number of catalyst modifications that can selectively improve the catalytic performance in target reactions. To date, many studies have been conducted to elucidate the effect of HAP modification on the catalytic activities for various reactions. However, systematic design strategies for HAP catalysts are not established yet due to an incomplete understanding of underlying structure-activity relationships. In this review, tuning methods of HAP for improving the catalytic performance are discussed: 1) ionic composition change, 2) morphology control, 3) incorporation of other metal species, and 4) catalytic support engineering. Detailed mechanisms and effects of structural modulations on the catalytic performances for attaining the design insights of HAP catalysts are investigated. In addition, computational studies to understand catalytic reactions on HAP materials are also introduced. Finally, important areas for future research are highlighted.

EFFECT OF MoO3 LOADING ON PRODUCT SELECTIVITY FOR CALCIUM PYROPHOSPHATE CATALYZED VAPOR PHASE LACTIC ACID DEHYDRATION

Calcium pyrophosphate and hydroxyapatite catalysts with varying C/P ratios have been previously used by our group for vapor phase dehydration of lactic acid to acrylic acid with almost 100% conversion and up to 78% acrylic acid selectivity. The activity was highly sensitive to acidity and basicity of the catalyst. Hence the catalyst with maximum activity, calcium pyrophosphate, was modified with MoO<sub>3</sub> for modifying its acidity and to study its effect on product selectivity for lactic acid dehydration. The MoO<sub>3</sub> modified calcium pyrophosphate with 5% MoO<sub>3</sub> loading was used for vapor phase dehydration of lactic acid at 375°C using 50% lactic acid concentration with WHSV of 3 h<sup>-1</sup>. The activity was compared with nonmodified calcium pyrophosphate catalyst. Surprisingly, deoxygenation was predominant compared to dehydration. Acidity was observed to play a crucial role in product selectivity (i.e,. with less acidic support, calcium pyrophosphate with 5 wt% MoO<sub>3</sub> showed more deoxygenation activity as compared to acidic support γ-Al<sub>2</sub>O<sub>3</sub> as well as SiO<sub>2</sub> with same MoO<sub>3</sub> loading). Higher acidity led to formation of acetaldehyde as the only product. The results confirmed formation of propionic acid by deoxygenation of lactic acid using in situ generated hydrogen after decarboxylation of lactic acid to acetaldehyde.

Influence of Ca/P ratio on the catalytic performance of hydroxyapatite for decarboxylation of itaconic acid to methacrylic acid

Methacrylic acid, an important organic chemical, is commercially manufactured starting from fossil feedstock. The decarboxylation of itaconic acid derived for biomass is a green route to the synthesis of methacrylic acid. In view of the problems existing in the researches on this route such as use of noble metal catalyst, harsh reaction conditions and low desired-product yield, we prepared a series of hydroxyapatite catalysts with different Ca/P molar ratios and evaluated their catalytic performance. The results showed that the hydroxyapatite catalyst with a Ca/P molar ratio of 1.58 had the best catalytic activity. The highest yield of MAA up to 61.2% was achieved with basically complete conversion of itaconic acid under the suitable reaction conditions of 1 equivalent of NaOH, 2 MPa of N2, 250 ℃, and 2 h. On this basis, a reaction network for the decarboxylation of itaconic acid to methacrylic acid catalyzed by hydroxyapatite was established. With the aid of catalyst characterization using X-ray powder diffraction, NH3/CO2 temperature-programmed desorption, N2 physisorption, inductively coupled plasma optical emission spectrometry, and scanning electron microscopy, we found that the distribution of surface acid sites and basic sites, crystal growth orientation, texture properties and morphology of hydroxyapatite varied with the Ca/P molar ratio. Furthermore, the change of the crystal growth orientation and its influence on the surface acidity and alkalinity were clarified.