Search

Graphical abstract Highlights • A facile method was developed to synthesize regenerable and H 2 O resistance sorbent for Hg0 removal. • The Ag nanoparticles were successively confined inside the mesoporous channels of MCM-41 molecule sieve. • The nanoconfinement effect is conducive to excellent Hg0 removal performance and regeneration ability. • The high hydrophobicity of Ag/MCM-41 is beneficial for the resistance to H 2 O. Abstract A facile passivation treatment and amino functionalized method was developed for controllable synthesis of effective and water-resistant Ag/MCM-41 composite sorbent for Hg0 removal in natural gas. The Ag nanoparticles were successively confined inside the mesoporous channels of MCM-41 molecule sieve with an average diameter of 3 nm. The synthesized sorbent was found to achieve a complete removal of Hg0 at high space velocity of 50,000 h−1 in ambient temperature. At 5% breakthrough, the Hg0 capture capacity of 1% (wt%) silver loaded Ag/MCM-41 was as high as 6.64 mg·g−1, which is much higher than the sample of Ag loaded outside of the pore channels (S-Ag/MCM-41) and other existing commercial sorbents. The H 2 O has negligible inhibitory effect on Hg0 removal performance of Ag/MCM-41. In addition, the spent Ag/MCM-41 could be easily regenerated without significant performance degradation over five cycles. We considered the high Hg0 capture efficiency, large adsorption capacity and excellent regeneration performance of Ag/MCM-41 are contributed to the nanoconfinement effect of mesoporous channels of MCM-41 molecule sieve which effectively prevented the growth and agglomeration of Ag nanoparticles. The good hydrophobicity of Ag/MCM-41 is beneficial for the high resistance to H 2 O. This work represents a giant step toward the preparation of effective sorbent for practical applications of Hg0 removal in natural gas. [ABSTRACT FROM AUTHOR]

A fixed-bed reactor was used to study the effect of water vapor on the efficiency of Hg 0 removal over CeO 2 -modified semi-coke. Adsorption experiments showed that the oxidation activity, and therefore, the mercury adsorption efficiency decreased with increasing water vapor concentrations. Hydrogen temperature-programmed reduction (H 2 -TPR) indicated that the oxidation activity of CeO 2 decreased after water vapor treatment. Fourier-transform infrared (FT-IR) studies revealed that CeO 2 -H 2 O showed new bending vibration peaks at 1110 cm −1 ascribed to Ce–OH groups. X-ray photoelectron spectroscopy (XPS) results showed that the content of Ce–OH increased from 20.85% to 39.99%, while the lattice oxygen content decreased from 68.21% to 45.83% after water vapor treatment. Density functional theory (DFT) calculations revealed that H 2 O can be dissociated on clean and oxygen-defective CeO 2 (1 1 1) surfaces to form H atoms and OH fragments. The H atoms associated with the adjacent oxygen atoms of CeO 2 , and the OH fragments were bound directly with Ce atoms to form Ce–OH for the clean CeO 2 surface; or occupied the oxygen vacancies and were surrounded by three Ce atoms via van der Waals forces, without additional bond formation for the oxygen-defective CeO 2 surface. Thus, the formation of Ce–OH groups and the consumption of lattice oxygens reduced the Hg 0 removal efficiency. [ABSTRACT FROM AUTHOR]

The silver loaded adsorbents has been demonstrated to be an exciting approach towards Hg 0 removal from natural gas streams, its Hg 0 removal efficiency and capacity is closely related to the valence state, particle size and dispersity of silver particles. This study focused on chemical reduction methods in aqueous solutions to synthesize Ag/4A zeolite, and the influences of ultrasonic and protective additives were investigated to reduce the size of silver particles. The characterization results showed that silver particles are loaded on the surface of 4A zeolite with highly dispersed elemental form, ultrasonic and addition of stearic acid as protective additives are the effective ways to produce small nano-scale silver particles close to 15 nm. Meanwhile, the silver particles on the surface of Ag/4A zeolite are the active sites for Hg 0 adsorption which can react with Hg 0 to form Ag-Hg amalgam alloy. The silver lattices disappeared from the outer boundary to the interior of the particles after Hg 0 adsorption, which indicated that the Hg 0 firstly reacts with the nano-scale silver on the surfaces and then gradually penetrates into the interior of silver particles. The Hg 0 removal efficiency of prepared Ag/4A zeolite adsorbents was higher than 96% after 200 min adsorption at 30 °C, and adsorption capacity reached to 5.985 mg/g. Furthermore, the regeneration and reutilization results indicated that the Hg 0 adsorption performance remained stable after 5 reuse cycles. [ABSTRACT FROM AUTHOR]