Insight into the promotional mechanism of Cu modification towards wide-temperature NH3-SCR performance of NbCe catalyst

A simple strategy of Cu modification was proposed to broaden the operation temperature window for NbCe catalyst.The best catalyst Cu0.010/Nb1Ce3 presented over 90%NO conversion in a wide temperature range of 200-400℃and exhibited an excellent H_(2)O or/and SO_(2) resistance at 275℃.To understand the promotional mechanism of Cu modification,the correlation among the"activity-structure-property"were tried to establish systematically.Cu species highly dispersed on NbCe catalyst to serve as the active component.The strong interaction among Cu,Nb and Ce promoted the emergence of NbO4 and induced more Bronsted acid sites.And Cu modification obviously enhanced the redox behavior of the NbCe catalyst.Besides,EPR probed the Cu species exited in the form of monomeric and dimeric Cu^(2+),the isolated Cu^(2+)acted as catalytic active sites to promote the reaction:Cu^(2+)-NO_(3)^(-)+NO(g)→Cu^(2+)-NO_(2)^(-)+NO_(2)(g).Then the generated NO_(2) would accelerate the fast-SCR reaction process and thus facilitated the lowtemperature deNO_(x) efficiency.Moreover,surface nitrates became unstable and easy to decompose after Cu modification,thus providing additional adsorption and activation sites for NH3,and ensuring the improvement of catalytic activity at high temperature.Since the NH3-SCR reaction followed by E-R reaction pathway efficaciously over Cu_(0.010)/Nb_(1)Ce_(3) catalyst,the excellent H_(2)O and SO_(2) resistance was as expected.

New analytic solutions to 2D transient heat conduction problems with/without heat sources in the symplectic space

The two-dimensional(2D)transient heat conduction problems with/without heat sources in a rectangular domain under different combinations of temperature and heat flux boundary conditions are studied by a novel symplectic superposition method(SSM).The solution process is within the Hamiltonian system framework such that the mathematical procedures in the symplectic space can be implemented,which provides an exceptional direct rigorous derivation without any assumptions or predetermination of the solution forms compared with the conventional inverse/semi-inverse methods.The distinctive advantage of the SSM offers an access to new analytic heat conduction solutions.The results obtained by the SSM agree well with those obtained from the finite element method(FEM),which confirms the accuracy of the SSM.

Effect of CeO_(2) nanoparticle sizes on catalytic performances of sulfated CeO_(2)/Al_(2)O_(3) catalyst in NH_(3)-SCR reaction

The sulfated CeO_(2)/Al_(2)O_(3) catalysts with different sizes of CeO_(2)nanoparticles were prepared by using pure H_2O or acetic acid solution as impregnation solvent, and the influence of sizes of CeO_(2) nanoparticles on the catalytic performances of the sulfated CeO_(2)/Al_(2)O_(3) catalyst was studied. The catalytic performance tests show that the sulfated CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution as impregnation solvent has better catalytic activity and the resistance to K+poisoning than the sulfated CeO_(2)/Al_(2)O_(3) catalyst using pure H_(2)O as impregnation solvent. The excellent catalytic performances can be ascribed to the smaller sizes of CeO_(2) nanoparticles in CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution, which results in larger amount of adsorbed sulfate species, surface acid sites, surface active oxygen species and excellent redox property. These features are helpful for improving the catalytic performances of sulfated CeO_(2)/Al_(2)O_(3) catalyst using smaller amount of CeO_(2) to cut the costs.

Deactivation induced by metal sulfate over MnCeOx catalyst in NH_(3)-SCR reaction at low temperature

Sulfate adsorption is one of the factors that cause the poisoning of catalyst in the low-temperature NH_(3) selective catalytic reduction reaction(NH_(3)-SCR).In this paper,by controlling the co-adsorption time of SO_(2) and O_(2) at 150℃,a range of sulfated MnCeOx catalysts with different contents of metal sulfate species were prepared to reveal the influence of metal sulfate species content on the catalytic performances and reaction mechanisms at low temperature.The catalytic activity below 250℃rapidly decreases with increasing metal sulfate species content.The results of characterizations shed light on the reduction of specific surface area,Mn^(4+)and Ce^(3+)content,and redox ability of MnCeOx owing to the formation of metal sulfate species.Further experiments reveal that metal sulfate species preferentially absorb on MnOx domains rather than on CeO_(2) domains,and the adsorbed metal sulfate species can suppress the Eley-Rideal and the Langmuir-Hinshelwood reaction mechanisms over the sulfated MnCeOx.All the above results are detrimental to the activity of sulfated MnCeOx in the low-temperature NH3-SCR reaction.