Effect of pore-size distribution on Ru/ZSM-5 catalyst for enhanced N2 activation to ammonia via dissociative mechanism

doi:10.1016/j.jre.2020.04.013

Journal of Rare Earths

Volume 38, Issue 8, August 2020, Pages 873-882

https://doi.org/10.1016/j.jre.2020.04.013 Get rights and content

Abstract

In the present study, a series of Ru/ZSM-5 catalysts with different pore-size distributions were prepared and investigated for NH₃ synthesis. Our studies indicate that Ru/ZSM-5-Mic with micropore structure exhibits superior NH₃ synthesis rate, which is much higher than those of Ru/ZSM-5-Mac (with macroporous structure) and Ru/ZSM-5-Mes (with mesoporous structure) catalysts. A series of TPD experiments demonstrate that pore-size distributions play an important role in N₂ adsorption and activation over Ru/ZSM-5. Moreover, the addition of La significantly promotes the NH₃ synthesis performance over Ru/ZSM-5-Mic. Additionally, in situ DRIFTS studies indicate that the main intermediate species over Ru/ZSM-5-Mic are –NH₂, and most of the surface hydrogen species desorb following the H₂O-formation pathway.

Graphical abstract

The pore-size distributions play an important role in NH₃ synthesis over Ru supported ZSM-5 catalyst. The effect of addition of La on Ru/ZSM-5-Mic for NH₃ synthesis was also investigated.

Introduction

Ammonia (NH₃) is the main source of nitrogenous fertilizer.¹ Most recently, NH₃ attracted much attention as an energy carrier in H₂ storage for its high capacity (17.6 wt%).² NH₃ synthesis has been realized in industrial production using Fe-based (e.g., Fe₃O₄ and Fe_1-xO) catalyst via Harber-Bosch process, which demands high temperature (400–600 °C) and high pressure (20–40 MPa).³^,⁴ In comparison to Fe-based catalysts, Ru-based catalysts can indeed lower the operation to 350–450 °C and ∼10 MPa. For instance, carbon-supported Ru catalysts have been successfully used in industry at pressure under 10 MPa.⁵ Nonetheless, any development that could lead to even milder conditions (<400 °C and <2 MPa) with increased catalytic performance is of importance in terms of scientific advancement and energy saving.⁶^,⁷

Zeolite is a crystalline porous solid with complex pores and channel system.⁸ Many studies have shown that the activity of catalysts supported on zeolites is greatly influenced by their pore structure.⁹^,¹⁰ For example, Pt catalysts supported on mesoporous zeolite exhibit more efficient catalytic performance than on microporous zeolites for the hydrodesulfurization of 4,6-dimethyldibenzothiophene. Furthermore, NH₃ synthesis performance of most Ru-based catalysts can be enhanced by promoters such as alkali metals, alkaline earth metals or rare earth metals.¹¹ The rare earth promoters in the Ru-based catalysts increase the catalytic performance by adjusting the balance between reducing the activation energy of N₂ dissociation and increasing the competitive adsorption of hydrogen.¹² Herein, comparative studies of Ru catalysts supported on ZSM-5 with different pore structures involving macroporous, mesoporous and microporous (named Ru/ZSM-5-Mac, Ru/ZSM-5-Mes and Ru/ZSM-5-Mic, respectively) for NH₃ synthesis were performed.

Section snippets

Catalyst preparation

In a typical synthesis of macroporous ZSM-5, 12.8 g of zeolite β (hydrogen), 1 g of NaAlO₂ (AR), 4 g of sillca gel (large pore) and 12 g of silicon dioxide solution (20 nm, 40 wt%) were mixed. The mixture was stirred at room temperature (RT) for 2 h. After drying at 110 °C for 24 h, the mixture was calcined at 550 °C for 4 h. Subsequently, 12 g of above mixture, 55 mg of NaOH (AR) and 3.3 g of TPABr (98%) were mixed in 27 mL of deionized water. The obtained solution was transferred into a

Structural and textural properties

Fig. 1 displays the N₂ physisorption isotherms and pore-size distributions over Ru/ZSM-5 with different pore-size distributions. Among them, the pore-size distributions of Ru/ZSM-5-Mes and Ru/ZSM-5-Mic were measured by N₂ adsorption according to the Barrett-Joyner-Halenda (BJH) method and Horvath-Kawazoe method, respectively, while Ru/ZSM-5-Mac was analysed through the pressurized mercury technique. N₂ adsorption/desorption isotherm profile of Ru/ZSM-5-Mac displays a step at a relative pressure

Conclusions

To summarize, a series of Ru/ZSM-5 catalysts with different pore-size distributions were prepared and investigated in NH₃ synthesis reaction. Our studies show that Ru/ZSM-5-Mic exhibits the highest catalytic performance for NH₃ synthesis with the lowest activation energies. Moreover, it is found that La can significantly promote NH₃ synthesis performance over Ru/ZSM-5-Mic. The co-existence of micropores structure over ZSM-5 and La species over Ru/La/ZSM-5-Mic accelerates the dissociation of N₂,

References (32)

K. Aika
Activation of nitrogen by alkali metal promoted transition metal I. Ammonia synthesis over ruthenium promoted by alkali metal
J Catal
(1972)
Y.Y. Shu et al.
Structure-sensitivity of hydrodesulfurization of 4,6-dimethyldibenzothiophene over silica-supported nickel phosphide catalysts
J Catal
(2005)
K. Aika et al.
Preparation and characterization of chlorine-free ruthenium catalysts and the promoter effect in ammonia synthesis: 3. a magnesia-supported ruthenium catalyst
J Catal
(1992)
S.E. Siporin et al.
Isotopic transient analysis of ammonia synthesis over Ru/MgO catalysts promoted by cesium, barium, or lanthanum
J Catal
(2004)
T. Zhang et al.
Selective catalytic reduction of NO with NH₃ over HZSM-5-supported Fe-Cu nanocomposite catalysts: the Fe-Cu bimetallic effect
Appl Catal, B
(2014)
F. Schmidt et al.
Coke location in microporous and hierarchical ZSM-5 and the impact on the MTH reaction
J Catal
(2013)
P.P. Knops-Gerrits et al.
Raman spectroscopy on zeolites
Microporous Mater
(1997)
S.Y. Mar et al.
Characterization of RuO₂ thin films by Raman spectroscopy
Appl Surf Sci
(1995)
J.X. Lin et al.
The effect of Ag as a promoter for Ru/CeO₂ catalysts in ammonia synthesis
J Mol Catal Chem
(2013)
A.A. Tsyganenko et al.
Infrared study of surface species arising from ammonia adsorption on oxide surfaces
J Mol Struct
(1975)

G. Ramis et al.

Ammonia activation over catalysts for the selective catalytic reduction of NO_x and the selective catalytic oxidation of NH₃. An FTIR study

Catal Today

(1996)

J.J. Max et al.

Aqueous ammonia and ammonium chloride hydrates: principal infrared spectra

J Mol Struct

(2013)

V. Smil

Detonator of the population explosion

Nature

(1999)

K. Nagaoka et al.

Carbon-free H₂ production from ammonia triggered at room temperature with an acidic RuO₂/gamma-Al₂O₃ catalyst

Sci Adv

(2017)

T. Kandemir et al.

The Haber-Bosch process revisited: on the real structure and stability of “Ammonia Iron” under working conditions

Angew Chem Int Ed

(2013)

D.E. Brown et al.

The genesis and development of the commercial BP doubly promoted catalyst for ammonia synthesis

Catal Lett

(2014)

Cited by (9)

Hydrogenation of NO<inf>x</inf> into ammonia under ambient conditions: From mechanistic investigation to multiphase catalysis
2023, Applied Catalysis B: Environmental
This work proposes a NOx recycling approach through nitrite hydrogenation into ammonia (NH₃/NH₄OH), and the screened out Pd⁰/Pd²⁺-loaded heterogeneous catalyst achieves excellent ammonia yield. Initially, the DFT calculation of nitrite hydrogenation was conducted to study the determining step for N₂/ammonia generation and guide the catalyst design. Consequently, the designed Pd^2+/0/ Covalent Triazine Framework (CTF) presented 100% nitrite conversion with 100% ammonia selectivity. The XPS and H₂-TPR results demonstrated the Pd²⁺/Pd⁰ ratios and Pd²⁺ reducibility greatly affected the nitrite conversion and ammonia selectivity. DRIFTs examined the reaction intermediates and the impact of Pd distribution behind ammonia generation. Under ambient conditions, a model test from NOx adsorption to ammonia release has been completed, and it exhibited an overall conversion of 70% NOx into ammonia in a single cycle with TOF of 3.9 h⁻¹, which proposes a direction of NOx recycling and utilization with less energy consumption and free of CO₂ emissions.
Hydrogenolysis of glycerol over ZSM-5 supported ruthenium and copper catalysts: Structural study and effects in reaction
2023, Catalysis Today
HZSM-5 supported bimetallic Ru-Cu catalysts were investigated with the objective of converting glycerol from biodiesel production into propanediols through the hydrogenolysis reaction. Two zeolites were used as supports, one with a SiO₂/Al₂O₃ molar ratio of 80 and another with a ratio of 23. Physisorption analysis showed high specific area for the solids with values in the range of 400 m² g⁻¹, that enabled the metals to be incorporated as nanoparticles undetectable by XRD. Monometallic Ru catalysts displayed Ru⁰ species after reduction and RuO₂ species duo to passivation, as evidenced by XPS analysis. Monometallic copper catalysts contained Cu⁰ and Cu⁺ species verified by XPS and DRIFTS after reduction and passivation, Cu²⁺ species were not found. As for the Ru-Cu bimetallic catalysts, Ru was added by impregnation of Cu/HZSM-5 and covered the copper nanoparticles as XPS analysis showed an increase in Ru/Cu molar ratio at the surface for both bimetallic catalysts. The XPS analysis showed increased Ru/Cu ratio at the surface for both bimetallic catalysts (1.95 and 2.94 for Ru-Cu/HZSM-5–80 and Ru-Cu/HZSM-5–23, respectively), furthermore no electronic effects between the two metals were observed indicating that the interaction between Ru and Cu consists in Ru diluting Cu. Chemisorption analysis show increase in CO adsorption for the bimetallic catalysts duo to the joint adsorptive capacity of Ru and Cu⁺, increasing from 141.4 µmol g⁻¹ to 147.8 µmol g⁻¹ for Ru-Cu/HZSM-5–80, and from 155.2 µmol g⁻¹ to 198.5 µmol g⁻¹ for Ru-Cu/HZSM-5–23, although the species adsorbed are thermally unstable compared to the monometallic adsorption, as shown by DRIFTS analysis. The activity of Ru catalysts was the highest (33 % and 32 % for catalysts supported on ZSM-5–80 and ZSM-5–23, respectively), but there was the formation of degradation products such as ethylene glycol. Copper catalysts showed moderate activity (11 % and 8 % for catalysts supported on ZSM-5–80 and ZSM-5–23, respectively) with good selectivity towards propanediols (22 % and 23 % for 1,2-PDO at isoconversion) duo to Cu⁰ and Cu⁺ interaction. Bimetallic catalysts Ru-Cu catalyst showed an improvement in selectivity to propanediols (36 % and 54 %) due to the interaction between Ru and Cu with low activity and reaction’s TOF (0.71 and 0.80 ×10⁻³ s⁻¹).
CeO<inf>2‒x</inf> modified Ru/γ-Al<inf>2</inf>O<inf>3</inf> catalysts for ammonia decomposition reaction
2023, Journal of Rare Earths
Developing high-performance ammonia decomposition catalysts for preparing CO_x-free hydrogen shows great practical significance. Herein, CeO₂ is used as a promoter to modulate the metal-support interaction to enhance the catalytic performance of Ru/Al₂O₃ catalysts. A series of 1Ru/xCe-10Al (x = 0.5, 1, or 3) catalysts was prepared by a facile colloidal deposition method. We find that the optimized 1Ru/1Ce–10Al catalyst exhibits excellent activity for the decomposition of ammonia with a very high hydrogen yield of 7097 mmol_H2/(g_Ru·min) at 450 °C. It is confirmed that Ru species are highly dispersed on the support surface as stable small clusters (∼1.3 nm). More importantly, due to the interaction between Ru species and partially reduced CeO_2–x, the electron density of Ru species is increased, which is beneficial to the high activity of the 1Ru/xCe-10Al catalysts. This work paves a way to construct high-efficiency ammonia decomposition catalysts modified by CeO₂.
A stable and efficient La-doped MIL-53(Al)/ZnO photocatalyst for sulfamethazine degradation
2022, Journal of Rare Earths
Citation Excerpt :
The position of the characteristic peaks of La 3d high-resolution spectra is the same as that of La-doped ZnO, and it can be concluded that La enters the lattice of ZnO. The SBET and pore structure were measured using N2 adsorption–desorption measurements, which can be used to compare adsorption capacity.35 Fig. 5(a) shows the results of each material.
Photocatalytic technology can solve various environmental pollution problems, especially antibiotic pollution. A novel La-doped MIL-53(Al)/ZnO composite material was successfully synthesized by a combination of hydrothermal method and calcination, showing high photocatalytic degradation percent of sulfamethazine (SMT). The 2 mol% La MIL-53(Al)/ZnO photocatalyst shows the highest degradation efficiency toward SMT (92%) within 120 min, which is 4.1 times higher than pure ZnO (increased from 18% to 92%). In addition, the degradation analysis of SMT by high performance liquid chromatography proves that the products are CO₂ and H₂O. The improved photocatalytic activity is mostly caused by the following factors. (1) Doping La ions can decrease the band gap of ZnO, enhance light response, and effectively enhance the separation rate of photo-generated holes and electrons. (2) MIL-53(Al) can adsorb SMT and promote the separation of electron. This work shows that the synthesized La-doped MIL-53(Al)/ZnO photocatalyst is expected to be used as a green and effective method for treatment of environment water pollution.
Combined Hydrogen and Alkane Production by Photocatalytic Decarboxylative C-C Homocoupling of Fatty Acid by Constructing a Hydrogen-Deficient Catalytic Interface
2024, ACS Catalysis
Study on kinetics of spent FCC catalyst applied to the living waste plastics
2023, Polymer Engineering and Science

View all citing articles on Scopus

^☆: Foundation item: Project supported by the National Natural Science Foundation of China (21972019).

View full text

Effect of pore-size distribution on Ru/ZSM-5 catalyst for enhanced N2 activation to ammonia via dissociative mechanism☆

Abstract

Graphical abstract

Introduction

Section snippets

Catalyst preparation

Structural and textural properties

Conclusions

J Catal

J Catal

J Catal

J Catal

Appl Catal, B

J Catal

Microporous Mater

Appl Surf Sci

J Mol Catal Chem

J Mol Struct

Catal Today

J Mol Struct

Detonator of the population explosion

Nature

Carbon-free H2 production from ammonia triggered at room temperature with an acidic RuO2/gamma-Al2O3 catalyst

Sci Adv

The Haber-Bosch process revisited: on the real structure and stability of “Ammonia Iron” under working conditions

Angew Chem Int Ed

The genesis and development of the commercial BP doubly promoted catalyst for ammonia synthesis

Catal Lett

Effect of pore-size distribution on Ru/ZSM-5 catalyst for enhanced N₂ activation to ammonia via dissociative mechanism☆

Carbon-free H₂ production from ammonia triggered at room temperature with an acidic RuO₂/gamma-Al₂O₃ catalyst