This work reports an exploratory study in terms of monoliths preparation for application in NOx CH4 selective catalytic reduction (NOx CH4-SCR), a promising route for treating the exhaust gas emissions from natural gas vehicles. By using washcoating method and a zeolite precursor, the effects of milling time (1, 2, or 16 h) and zeolite concentration in the slurry (15, 20, or 30 wt %) on the coating characteristics were evaluated. Then, the optimized washcoating conditions were used in order to obtain two PdCe-HMOR zeolite-coated monoliths with different number of CPSI (400 or 600). Tests were carried out under representative conditions of real exhaust gases from a heavy duty vehicle's engine. Results showed that the differences in the performances of both materials could not be attributed to hydrodynamic factors being thus proposed an explanation related to the catalyst surface area in contact with the inlet feed gas, significantly higher for the most active monolith.